/*@jsxRuntime automatic @jsxImportSource react*/ const {Fragment: _Fragment, jsx: _jsx, jsxs: _jsxs} = arguments[0]; const {useMDXComponents: _provideComponents} = arguments[0]; function _createMdxContent(props) { const _components = Object.assign({ h2: "h2", p: "p", ul: "ul", li: "li", a: "a", h3: "h3", h4: "h4", figure: "figure", pre: "pre", code: "code", span: "span", h5: "h5", strong: "strong", blockquote: "blockquote" }, _provideComponents(), props.components), {References, Alert, CodeVariants, CodeVariant} = _components; if (!Alert) _missingMdxReference("Alert", true); if (!CodeVariant) _missingMdxReference("CodeVariant", true); if (!CodeVariants) _missingMdxReference("CodeVariants", true); if (!References) _missingMdxReference("References", true); return _jsxs(_Fragment, { children: [_jsx(_components.h2, { id: "introduction", children: "Introduction" }), "\n", _jsx(_components.p, { children: "Functional Programming offers valuable concepts that can enhance our code quality and maintainability. By using immutable data structures and pure functions, we can reduce side effects, making our code more predictable and easier to debug.\nWe will dig into the basics, covering the following topics:" }), "\n", _jsxs(_components.ul, { children: ["\n", _jsxs(_components.li, { children: [_jsx(_components.a, { href: "#immutability", children: "Immutability" }), " - State management."] }), "\n", _jsxs(_components.li, { children: [_jsx(_components.a, { href: "#functions", children: "Functions" }), " - Functional programming fundament."] }), "\n", _jsxs(_components.li, { children: [_jsx(_components.a, { href: "#optional", children: "Monads" }), " - Wrappers for side effects."] }), "\n"] }), "\n", _jsx(_components.h3, { id: "immutability", children: "Immutability" }), "\n", _jsx(_components.p, { children: "The primary concept with which we may already be familiar is immutability. Immutability ensures that data remains consistent and predictable, making it easier to reason about the state of an application." }), "\n", _jsx(_components.h4, { id: "immutable-objects", children: "Immutable objects" }), "\n", _jsx(_components.p, { children: "Immutable objects, once created, cannot be modified. They remain the same throughout their entire life cycle." }), "\n", _jsx(_components.figure, { "data-rehype-pretty-code-figure": "", children: _jsx(_components.pre, { style: { backgroundColor: "#ffffff", color: "#24292eff" }, tabIndex: "0", "data-language": "java", "data-theme": "min-light", children: _jsxs(_components.code, { "data-language": "java", "data-theme": "min-light", style: { display: "grid" }, children: [_jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#C2C3C5" }, children: "// old fashion way" }) }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: "public" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " class" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " Reservation" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " private" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " final" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " ReservationId" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " id;" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " private" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " final" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " ReservationStatus" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " status;" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: " " }) }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " public" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " Reservation" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "ReservationId" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " id" }), _jsx(_components.span, { style: { color: "#212121" }, children: "," }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " ReservationStatus" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " status) {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#1976D2" }, children: " this" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#1976D2" }, children: "id" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " =" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " id;" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#1976D2" }, children: " this" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#1976D2" }, children: "status" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " =" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " status;" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: " }" }) }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: " " }) }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#C2C3C5" }, children: " // getters" }) }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#C2C3C5" }, children: " // equals & hashCode" }) }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: "}" }) })] }) }) }), "\n", _jsx(_components.p, { children: "For years, Java has not had a decent built-in way of defining immutable objects, but we live to see records." }), "\n", _jsx(_components.figure, { "data-rehype-pretty-code-figure": "", children: _jsx(_components.pre, { style: { backgroundColor: "#ffffff", color: "#24292eff" }, tabIndex: "0", "data-language": "java", "data-theme": "min-light", children: _jsxs(_components.code, { "data-language": "java", "data-theme": "min-light", style: { display: "grid" }, children: [_jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#C2C3C5" }, children: "// Java 14+" }) }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: "public" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " record" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " Reservation" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "ReservationId" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " id" }), _jsx(_components.span, { style: { color: "#212121" }, children: "," }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " ReservationStatus" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " status) {" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: "}" }) })] }) }) }), "\n", _jsx(References, { links: [{ title: "Record Classes", url: "https://docs.oracle.com/en/java/javase/17/language/records.html" }] }), "\n", _jsx(_components.p, { children: "The following code doesn't allow us any modification,\nthe only way to \"update\" the object is to create a new one with changed values." }), "\n", _jsx(_components.figure, { "data-rehype-pretty-code-figure": "", children: _jsx(_components.pre, { style: { backgroundColor: "#ffffff", color: "#24292eff" }, tabIndex: "0", "data-language": "java", "data-theme": "min-light", children: _jsxs(_components.code, { "data-language": "java", "data-theme": "min-light", style: { display: "grid" }, children: [_jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: "public" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " record" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " Reservation" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "ReservationId" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " id" }), _jsx(_components.span, { style: { color: "#212121" }, children: "," }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " ReservationStatus" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " status) {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " Reservation" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " cancel" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "() {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " return" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " new" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " Reservation(id" }), _jsx(_components.span, { style: { color: "#212121" }, children: "," }), _jsx(_components.span, { style: { color: "#1976D2" }, children: " ReservationStatus" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#1976D2" }, children: "Cancelled" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: ")" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ";" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: " }" }) }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: "}" }) })] }) }) }), "\n", _jsx(_components.p, { children: "What are the main benefits of using immutable objects?" }), "\n", _jsxs(_components.ul, { children: ["\n", _jsx(_components.li, { children: "Immutable objects are thread-safe, they can be shared among multiple threads without restraint." }), "\n", _jsx(_components.li, { children: "Allows you to reason about a piece of code independently of the rest of the program because our internal state can't be changed by another part of our system." }), "\n", _jsx(_components.li, { children: "We can model things like they are, e.g. events - the fact already happened we can't change past." }), "\n"] }), "\n", _jsx(_components.h4, { id: "immutable-collections", children: "Immutable collections" }), "\n", _jsxs(_components.p, { children: ["Immutable collections, like immutable objects, cannot be updated after creation.\nThe only way to add or remove an element is to create a new collection instance.\nImmutable List in Java can be created using ", _jsx(_components.code, { children: "List.of(\"a\", \"b\", \"c\")" }), ",\nany modification on this list will cause an exception."] }), "\n", _jsx(_components.h5, { id: "immutable-vs-mutable-collections", children: "Immutable vs Mutable collections" }), "\n", _jsxs(_components.p, { children: ["We'll start with the main problem of mutable collections: they ", _jsx(_components.strong, { children: "can be modified by anyone" }), "."] }), "\n", _jsx(_components.figure, { "data-rehype-pretty-code-figure": "", children: _jsx(_components.pre, { style: { backgroundColor: "#ffffff", color: "#24292eff" }, tabIndex: "0", "data-language": "java", "data-theme": "min-light", children: _jsxs(_components.code, { "data-language": "java", "data-theme": "min-light", style: { display: "grid" }, children: [_jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: "ShowStats" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " getShowStats(" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "List<" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "Reservation" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: ">" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " reservations)" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " int" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " activeReservations " }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "=" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " calculateActiveReservations(reservations)" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ";" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " int" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " totalReservations " }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "=" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: " reservations" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "size" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "();" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " return" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " new" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " ShowStats(activeReservations" }), _jsx(_components.span, { style: { color: "#212121" }, children: "," }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " totalReservations)" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ";" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: "}" }) })] }) }) }), "\n", _jsxs(_components.p, { children: ["At first glance, it looks fine, but what if ", _jsx(_components.code, { children: "calculateActiveReservations()" }), " removes some elements from the provided list?"] }), "\n", _jsx(_components.figure, { "data-rehype-pretty-code-figure": "", children: _jsx(_components.pre, { style: { backgroundColor: "#ffffff", color: "#24292eff" }, tabIndex: "0", "data-language": "java", "data-theme": "min-light", children: _jsxs(_components.code, { "data-language": "java", "data-theme": "min-light", style: { display: "grid" }, children: [_jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: "public" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " int" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " calculateActiveReservations(" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "List<" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "Reservations" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: ">" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " reservations)" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#1976D2" }, children: " reservations" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "removeIf" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(reservation " }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "->" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: " reservation" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "getStatus" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "() " }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "!=" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: " Status" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#1976D2" }, children: "Active" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ");" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " return" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: " reservations" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "size" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "();" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: "}" }) })] }) }) }), "\n", _jsxs(_components.p, { children: ["If we pass an ", _jsx(_components.code, { children: "ArrayList" }), " the method will modify the list and that will cause a bug"] }), "\n", _jsx(_components.figure, { "data-rehype-pretty-code-figure": "", children: _jsx(_components.pre, { style: { backgroundColor: "#ffffff", color: "#24292eff" }, tabIndex: "0", "data-language": "java", "data-theme": "min-light", children: _jsxs(_components.code, { "data-language": "java", "data-theme": "min-light", style: { display: "grid" }, children: [_jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: "ShowStats" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " getShowStats(" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "List<" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "Reservation" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: ">" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " reservations)" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " { " })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#C2C3C5" }, children: " // reservations = [Reservation[status=Active], Reservation[status=Active], Reservation[status=Cancelled]]" }) }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " int" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " activeReservations " }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "=" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " calculateActiveReservations(reservations)" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "; " }), _jsx(_components.span, { style: { color: "#C2C3C5" }, children: "// " })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#C2C3C5" }, children: " // reservations = [Reservation[status=Active], Reservation[status=Active]]" }) }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " int" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " totalReservations " }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "=" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: " reservations" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "size" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(); " }), _jsx(_components.span, { style: { color: "#C2C3C5" }, children: "// 2" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " return" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " new" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " ShowStats(activeReservations" }), _jsx(_components.span, { style: { color: "#212121" }, children: "," }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " totalReservations)" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ";" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: "}" }) })] }) }) }), "\n", _jsxs(_components.p, { children: ["If we create a list using ", _jsx(_components.code, { children: "List.of()" }), " or ", _jsx(_components.code, { children: "Stream#toList()" }), " it will create ", _jsx(_components.code, { children: "ImmutableCollections.List" }), ",\nwhich doesn't allow any modification and informs us about that through a ", _jsx(_components.code, { children: "UnusportedOperationException" }), "."] }), "\n", _jsx(_components.figure, { "data-rehype-pretty-code-figure": "", children: _jsx(_components.pre, { style: { backgroundColor: "#ffffff", color: "#24292eff" }, tabIndex: "0", "data-language": "java", "data-theme": "min-light", children: _jsxs(_components.code, { "data-language": "java", "data-theme": "min-light", style: { display: "grid" }, children: [_jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: "public" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " int" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " calculateActiveReservations(" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "List<" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "Reservations" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: ">" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " reservations)" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " { " }), _jsx(_components.span, { style: { color: "#C2C3C5" }, children: "// List.of();" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#1976D2" }, children: " reservations" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "removeIf" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(reservation " }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "->" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: " reservation" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "getStatus" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "() " }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "!=" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: " Status" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#1976D2" }, children: "Active" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "); " }), _jsx(_components.span, { style: { color: "#C2C3C5" }, children: "// UnsupportedOperationException" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " return" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: " reservations" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "size" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "();" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: "}" }) })] }) }) }), "\n", _jsx(_components.p, { children: "But there are a few problems with standard \"immutable\" Java collections:" }), "\n", _jsxs(_components.ul, { children: ["\n", _jsx(_components.li, { children: "The behavior seems more like read-only than immutable. Immutable collections should return us a copy." }), "\n", _jsx(_components.li, { children: "Informs about illegal operations at runtime." }), "\n"] }), "\n", _jsx(_components.p, { children: "So let's see how else we can approach the subject." }), "\n", _jsxs(_components.p, { children: ["For example, In Kotlin ", _jsx(_components.code, { children: "List" }), " interface doesn't contain methods like ", _jsx(_components.code, { children: "add" }), ", ", _jsx(_components.code, { children: "remove" }), ", etc.\nAnd that sounds much more reasonable than throwing ", _jsx(_components.code, { children: "UnsupportedOperationException" }), ",\nbecause we are held back by the compiler during at the development stage."] }), "\n", _jsx(_components.figure, { "data-rehype-pretty-code-figure": "", children: _jsx(_components.pre, { style: { backgroundColor: "#ffffff", color: "#24292eff" }, tabIndex: "0", "data-language": "kotlin", "data-theme": "min-light", children: _jsxs(_components.code, { "data-language": "kotlin", "data-theme": "min-light", style: { display: "grid" }, children: [_jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: "val" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " immutableList: " }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "List" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "<" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "String" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "> " }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "=" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " arrayListOf" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(" }), _jsx(_components.span, { style: { color: "#22863A" }, children: "\"a\"" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ")" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#24292EFF" }, children: "immutableList." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "add" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(" }), _jsx(_components.span, { style: { color: "#22863A" }, children: "\"b\"" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ") " }), _jsx(_components.span, { style: { color: "#C2C3C5" }, children: "// doesn't work, there is no method like 'add'" })] })] }) }) }), "\n", _jsxs(_components.p, { children: ["To modify a list we need to define it explicitly as ", _jsx(_components.code, { children: "MutableList" })] }), "\n", _jsx(_components.figure, { "data-rehype-pretty-code-figure": "", children: _jsx(_components.pre, { style: { backgroundColor: "#ffffff", color: "#24292eff" }, tabIndex: "0", "data-language": "kotlin", "data-theme": "min-light", children: _jsxs(_components.code, { "data-language": "kotlin", "data-theme": "min-light", style: { display: "grid" }, children: [_jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: "val" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " mutableList: " }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "MutableList" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "<" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "String" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "> " }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "=" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " arrayListOf" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(" }), _jsx(_components.span, { style: { color: "#22863A" }, children: "\"a\"" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ")" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#24292EFF" }, children: "mutableList." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "add" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(" }), _jsx(_components.span, { style: { color: "#22863A" }, children: "\"b\"" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ")" })] })] }) }) }), "\n", _jsx(_components.p, { children: "It's better, but not perfect. Adding elements should be allowed,\nbut it should create a new list containing values from the source list and the newly added value." }), "\n", _jsx(_components.p, { children: "But won't it be slow?\nTheoretically, yes, but actually no.\nThe collection size is usually small, so it doesn't really matter.\nAdditionally, we don't have to copy all values to the new list." }), "\n", _jsx(_components.p, { children: "Instead, when we add a value, we create a new object that contains a reference to the previous object along with the new element." }), "\n", _jsx(_components.figure, { "data-rehype-pretty-code-figure": "", children: _jsx(_components.pre, { style: { backgroundColor: "#ffffff", color: "#24292eff" }, tabIndex: "0", "data-language": "java", "data-theme": "min-light", children: _jsxs(_components.code, { "data-language": "java", "data-theme": "min-light", style: { display: "grid" }, children: [_jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: "class" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " ImmutableList" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "<" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "T" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "> {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " private" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " ImmutableList" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "<" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "T" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "> head;" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " private" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " T" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " tail;" })] }), "\n", _jsx(_components.span, { "data-line": "", children: " " }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " ImmutableList" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "<" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "T" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "> " }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "add" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "T" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " element) {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " return" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " new" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " ImmutableList" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "<>(" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: "this" }), _jsx(_components.span, { style: { color: "#212121" }, children: "," }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " element);" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: " }" }) }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: "}" }) })] }) }) }), "\n", _jsx(References, { links: [{ title: "io.vavr.collection.List.java", url: "https://github.com/vavr-io/vavr/blob/master/src/main/java/io/vavr/collection/List.java" }] }), "\n", _jsx(_components.p, { children: "Unfortunately, such collections are not built in Java, so we need to use external libraries like Vavr.io" }), "\n", _jsx(_components.h3, { id: "functions", children: "Functions" }), "\n", _jsx(_components.p, { children: "Functional programming is all about programming with functions.\nFunctions are:" }), "\n", _jsxs(_components.ul, { children: ["\n", _jsx(_components.li, { children: "Total. For every input, they return an output." }), "\n", _jsx(_components.li, { children: "Pure. The function return values are identical for identical arguments, and the function has no side effects." }), "\n"] }), "\n", _jsx(_components.p, { children: "Let's review a few methods and determine if they are total and pure." }), "\n", _jsx(_components.figure, { "data-rehype-pretty-code-figure": "", children: _jsx(_components.pre, { style: { backgroundColor: "#ffffff", color: "#24292eff" }, tabIndex: "0", "data-language": "java", "data-theme": "min-light", children: _jsxs(_components.code, { "data-language": "java", "data-theme": "min-light", style: { display: "grid" }, children: [_jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: "class" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " Account" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " private" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " BigDecimal" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " balance;" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: " " }) }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " void" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " deposit" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "BigDecimal" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " amount) {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " if" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " (amount " }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "<=" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: " 0" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ") {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " throw" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " new" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " IllegalArgumentException()" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ";" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: " }" }) }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#24292EFF" }, children: " balance " }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "+=" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " amount;" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: " }" }) }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: "}" }) })] }) }) }), "\n", _jsxs(Alert, { type: 'tip', children: [_jsxs(_components.p, { children: ["As a rule of thumb, using ", _jsx(_components.code, { children: "void" }), " is usually bad practice.\nMethods that return void:"] }), _jsxs(_components.ul, { children: ["\n", _jsx(_components.li, { children: "cannot be used in method chaining." }), "\n"] }), _jsx(_components.figure, { "data-rehype-pretty-code-figure": "", children: _jsx(_components.pre, { style: { backgroundColor: "#ffffff", color: "#24292eff" }, tabIndex: "0", "data-language": "java", "data-theme": "min-light", children: _jsxs(_components.code, { "data-language": "java", "data-theme": "min-light", style: { display: "grid" }, children: [_jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#1976D2" }, children: "account" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "map" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(ac " }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "->" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#1976D2" }, children: " ac" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "deposit" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: "BigDecimal" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "of" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: "10" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "));" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " return" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " ac;" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: "});" }) })] }) }) }), _jsxs(_components.ul, { children: ["\n", _jsx(_components.li, { children: "Force to use exceptions for error handling." }), "\n", _jsx(_components.li, { children: "Are harder to test." }), "\n", _jsx(_components.li, { children: "Make it more difficult to track changes that have been made." }), "\n"] })] }), "\n", _jsx(_components.p, { children: "It's not total nor pure.\nThe method returns output only if the argument is greater than 0, and it modifies the internal state,\nso depending on the current state the method may behave differently." }), "\n", _jsx(_components.p, { children: "To make it total, we can introduce a new type that allows only to provide positive BigDecimals.\nSo now our method signature forces us to use the appropriate parameter." }), "\n", _jsx(_components.figure, { "data-rehype-pretty-code-figure": "", children: _jsx(_components.pre, { style: { backgroundColor: "#ffffff", color: "#24292eff" }, tabIndex: "0", "data-language": "java", "data-theme": "min-light", children: _jsxs(_components.code, { "data-language": "java", "data-theme": "min-light", style: { display: "grid" }, children: [_jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: "void" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " deposit(" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "PositiveBigDecimal" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " amount)" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#24292EFF" }, children: " balance " }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "+=" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " amount;" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: "}" }) })] }) }) }), "\n", _jsx(_components.p, { children: "Let's try to make it also pure.\nWhat if we make this object immutable?" }), "\n", _jsx(_components.figure, { "data-rehype-pretty-code-figure": "", children: _jsx(_components.pre, { style: { backgroundColor: "#ffffff", color: "#24292eff" }, tabIndex: "0", "data-language": "java", "data-theme": "min-light", children: _jsxs(_components.code, { "data-language": "java", "data-theme": "min-light", style: { display: "grid" }, children: [_jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: "class" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " Account" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " private" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " final" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " BigDecimal" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " balance;" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: " " }) }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " Account" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " deposit" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "BigDecimal" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " amount) {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " return" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " new" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " Account(balance " }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "+" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " amount)" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ";" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: " }" }) }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: "}" }) })] }) }) }), "\n", _jsx(_components.p, { children: "You may say it's still not pure because it still depends on the internal state.\nBut what if we write it down like this:" }), "\n", _jsx(_components.figure, { "data-rehype-pretty-code-figure": "", children: _jsx(_components.pre, { style: { backgroundColor: "#ffffff", color: "#24292eff" }, tabIndex: "0", "data-language": "java", "data-theme": "min-light", children: _jsxs(_components.code, { "data-language": "java", "data-theme": "min-light", style: { display: "grid" }, children: [_jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: "static" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " Account" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " deposit(" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "Account" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " account" }), _jsx(_components.span, { style: { color: "#212121" }, children: "," }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " BigDecimal" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " amount)" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " return" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " new" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " Account(" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: "account" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "balance() " }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "+" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " amount)" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ";" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: "}" }) })] }) }) }), "\n", _jsx(_components.p, { children: "As you see, we can just treat our object as the first argument of our function.\nSo the first approach is absolutely fine and can be acknowledged as pure.\nLet's take a look at another example:" }), "\n", _jsx(_components.figure, { "data-rehype-pretty-code-figure": "", children: _jsx(_components.pre, { style: { backgroundColor: "#ffffff", color: "#24292eff" }, tabIndex: "0", "data-language": "java", "data-theme": "min-light", children: _jsxs(_components.code, { "data-language": "java", "data-theme": "min-light", style: { display: "grid" }, children: [_jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: "private" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " Map" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "<" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "Long" }), _jsx(_components.span, { style: { color: "#212121" }, children: "," }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " User" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "> users " }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "=" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " new" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " HashMap" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "<>();" })] }), "\n", _jsx(_components.span, { "data-line": "", children: " " }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: "User" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " getUser(" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "long" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " id)" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " return" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: " users" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "get" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(id);" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: "}" }) })] }) }) }), "\n", _jsx(_components.p, { children: "Is the function pure?\nIt's not, It can return User or null for the same argument." }), "\n", _jsxs(_components.p, { children: ["How can we fix it? We can present it explicitly using a type system.\nIn this case ", _jsx(_components.code, { children: "Optional" }), " seems reasonable."] }), "\n", _jsx(_components.figure, { "data-rehype-pretty-code-figure": "", children: _jsx(_components.pre, { style: { backgroundColor: "#ffffff", color: "#24292eff" }, tabIndex: "0", "data-language": "java", "data-theme": "min-light", children: _jsxs(_components.code, { "data-language": "java", "data-theme": "min-light", style: { display: "grid" }, children: [_jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: "Optional<" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "User" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: ">" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " getUser(" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "long" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " id)" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " return" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: " Optional" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "ofNullable" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: "map" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "get" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(id));" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: "} " }) })] }) }) }), "\n", _jsx(_components.p, { children: "The side effect still exists, but we encoded that fact using type system.\nIt's not hidden like in the previous example." }), "\n", _jsx(_components.h4, { id: "optional", children: "Optional" }), "\n", _jsxs(_components.p, { children: ["For those not familiar with FP the most straightforward way to use ", _jsx(_components.code, { children: "Optional" }), " will be"] }), "\n", _jsx(_components.figure, { "data-rehype-pretty-code-figure": "", children: _jsx(_components.pre, { style: { backgroundColor: "#ffffff", color: "#24292eff" }, tabIndex: "0", "data-language": "java", "data-theme": "min-light", children: _jsxs(_components.code, { "data-language": "java", "data-theme": "min-light", style: { display: "grid" }, children: [_jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: "Optional" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "<" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "User" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "> userOpt " }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "=" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " getUser(" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: "1" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: ")" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ";" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: "if" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " (" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: "userOpt" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "isPresent" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "()) {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " User" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " user " }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "=" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: " userOpt" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "get" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(); " })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: "}" }) })] }) }) }), "\n", _jsxs(_components.p, { children: ["But it's not really how we do it functionally.\nIn most cases, we should avoid invoking ", _jsx(_components.code, { children: "get()" }), ".\nWe want to use ", _jsx(_components.code, { children: "map" }), " and ", _jsx(_components.code, { children: "flatMap" }), " operations."] }), "\n", _jsxs(CodeVariants, { tabs: false, children: [_jsx(CodeVariant, { name: "Bad ❌", children: _jsx(_components.figure, { "data-rehype-pretty-code-figure": "", children: _jsx(_components.pre, { style: { backgroundColor: "#ffffff", color: "#24292eff" }, tabIndex: "0", "data-language": "java", "data-theme": "min-light", children: _jsxs(_components.code, { "data-language": "java", "data-theme": "min-light", style: { display: "grid" }, children: [_jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: "public" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " String" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " displayUsername(" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "long" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " userId)" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " Optional" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "<" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "User" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "> userOpt " }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "=" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " getUser(userId)" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ";" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " if" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " (" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: "userOpt" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "isPresent" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "()) {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " return" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: " userOpt" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "get" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "()" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "getName" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "();" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: " }" }) }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " return" }), _jsx(_components.span, { style: { color: "#22863A" }, children: " \"Anonymous\"" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ";" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: "}" }) })] }) }) }) }), _jsx(CodeVariant, { name: "Good ✅", children: _jsx(_components.figure, { "data-rehype-pretty-code-figure": "", children: _jsx(_components.pre, { style: { backgroundColor: "#ffffff", color: "#24292eff" }, tabIndex: "0", "data-language": "java", "data-theme": "min-light", children: _jsxs(_components.code, { "data-language": "java", "data-theme": "min-light", style: { display: "grid" }, children: [_jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: "public" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " String" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " displayUsername(" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "long" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " userId)" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " return" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " getUser(userId)" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#212121" }, children: " ." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "map" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(user " }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "->" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: " user" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "getName" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "())" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#212121" }, children: " ." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "orElse" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(" }), _jsx(_components.span, { style: { color: "#22863A" }, children: "\"Anonymous\"" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ");" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: "}" }) }), "\n", _jsx(_components.span, { "data-line": "", children: " " }), "\n", _jsx(_components.span, { "data-line": "", children: " " })] }) }) }) })] }), "\n", _jsxs(_components.p, { children: ["The first piece of code is not perfect, but we can live with it.\nLet's imagine ", _jsx(_components.code, { children: "User#getUsername" }), " returns ", _jsx(_components.code, { children: "Optional" })] }), "\n", _jsxs(CodeVariants, { tabs: false, children: [_jsx(CodeVariant, { name: "Bad ❌", children: _jsx(_components.figure, { "data-rehype-pretty-code-figure": "", children: _jsx(_components.pre, { style: { backgroundColor: "#ffffff", color: "#24292eff" }, tabIndex: "0", "data-language": "java", "data-theme": "min-light", children: _jsxs(_components.code, { "data-language": "java", "data-theme": "min-light", style: { display: "grid" }, children: [_jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: "public" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " String" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " displayUsername(" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "long" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " userId)" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " Optional" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "<" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "User" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "> userOpt " }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "=" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " getUser(userId)" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ";" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: 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{ style: { color: "#6F42C1" }, children: "get" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "();" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: " }" }) }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: " }" }) }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " return" }), _jsx(_components.span, { style: { color: "#22863A" }, children: " \"Anonymous\"" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ";" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: "}" }) })] }) }) }) }), _jsx(CodeVariant, { name: "Good ✅", children: _jsx(_components.figure, { "data-rehype-pretty-code-figure": "", children: _jsx(_components.pre, { style: { backgroundColor: "#ffffff", color: "#24292eff" }, tabIndex: "0", "data-language": "java", "data-theme": "min-light", children: _jsxs(_components.code, { "data-language": "java", "data-theme": "min-light", style: { display: "grid" }, children: [_jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: "public" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " String" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " displayUsername(" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "long" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " userId)" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " return" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " getUser(userId)" })] }), "\n", _jsxs(_components.span, { "data-line": "", "data-highlighted-line": "", children: [_jsx(_components.span, { style: { color: "#212121" }, children: " ." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "flatMap" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(user " }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "->" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: " user" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "getName" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "()) " })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#212121" }, children: " ." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "orElse" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(" }), _jsx(_components.span, { style: { color: "#22863A" }, children: "\"Anonymous\"" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "); " })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: "}" }) }), "\n", _jsx(_components.span, { "data-line": "", children: " " }), "\n", _jsx(_components.span, { "data-line": "", children: " " }), "\n", _jsx(_components.span, { "data-line": "", children: " " }), "\n", _jsx(_components.span, { "data-line": "", children: " " }), "\n", _jsx(_components.span, { "data-line": "", children: " " })] }) }) }) })] }), "\n", _jsx(_components.h4, { id: "validation", children: "Validation" }), "\n", _jsx(_components.p, { children: "The hidden behavior also applies to validation." }), "\n", _jsx(_components.figure, { "data-rehype-pretty-code-figure": "", children: _jsx(_components.pre, { style: { backgroundColor: "#ffffff", color: "#24292eff" }, tabIndex: "0", "data-language": "java", "data-theme": "min-light", children: _jsxs(_components.code, { "data-language": "java", "data-theme": "min-light", style: { display: "grid" }, children: [_jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: "public" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " User" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " createUser(" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "String" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " name)" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " if" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " (" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: "name" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#1976D2" }, children: "length" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " <" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: " 3" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ") {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " throw" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " new" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " IllegalArgumentException(" }), _jsx(_components.span, { style: { color: "#22863A" }, children: "\"Name too short\"" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: ")" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ";" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: " }" }) }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " return" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " new" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " User(name)" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ";" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: "}" }) })] }) }) }), "\n", _jsx(_components.p, { children: "What's the problem here?" }), "\n", _jsxs(_components.ul, { children: ["\n", _jsx(_components.li, { children: "The method signature hides from us the fact there is validation inside the method body." }), "\n", _jsx(_components.li, { children: "The compiler doesn't force us to handle errors." }), "\n", _jsxs(_components.li, { children: ["Exceptions are not an excellent choice for business errors, they are more for ", _jsx(_components.strong, { children: "exception" }), "al cases."] }), "\n"] }), "\n", _jsx(_components.p, { children: "How to do it in a better way?" }), "\n", _jsx(_components.figure, { "data-rehype-pretty-code-figure": "", children: _jsx(_components.pre, { style: { backgroundColor: "#ffffff", color: "#24292eff" }, tabIndex: "0", "data-language": "java", "data-theme": "min-light", children: _jsxs(_components.code, { "data-language": "java", "data-theme": "min-light", style: { display: "grid" }, children: [_jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: "public" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " Either<" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "DomainError" }), _jsx(_components.span, { style: { color: "#212121" }, children: "," }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " User" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: ">" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " createUser(" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "String" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " name)" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " if" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " (" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: "name" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#1976D2" }, children: "length" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " <" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: " 3" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ") {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " return" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: " Either" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "left" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: "DomainError" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#1976D2" }, children: "NAME_TOO_SHORT" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ");" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: " }" }) }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " return" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: " Either" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "right" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "new" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " User(name)" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ");" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: "}" }) })] }) }) }), "\n", _jsx(_components.p, { children: "Either allows explicitly showing our method has two paths.\nThe success - right, and the failure - left." }), "\n", _jsx(References, { links: [{ title: "Either", url: "https://eed3si9n.com/learning-scalaz/Either.html" }] }), "\n", _jsx(_components.p, { children: "Thanks to that:" }), "\n", _jsxs(_components.ul, { children: ["\n", _jsx(_components.li, { children: "There's no need to examine the method code to identify alternative scenarios." }), "\n", _jsx(_components.li, { children: "compiler forces us to handle errors." }), "\n"] }), "\n", _jsxs(_components.p, { children: ["Another interesting class is ", _jsx(_components.code, { children: "Validation" }), ". Like ", _jsx(_components.code, { children: "Either" }), ", ", _jsx(_components.code, { children: "Validation" }), " contains two paths, valid and invalid.\nThe main difference is that instead of chaining the result from the first event to the next, ", _jsx(_components.code, { children: "Validation" }), " validates all events."] }), "\n", _jsx(References, { links: [{ title: "Validation", url: "https://eed3si9n.com/learning-scalaz/Validation.html" }] }), "\n", _jsx(_components.p, { children: "To demonstrate the usage, let's write a code for loading CSV files." }), "\n", _jsx(_components.figure, { "data-rehype-pretty-code-figure": "", children: _jsx(_components.pre, { style: { backgroundColor: "#ffffff", color: "#24292eff" }, tabIndex: "0", "data-language": "java", "data-theme": "min-light", children: _jsxs(_components.code, { "data-language": "java", "data-theme": "min-light", style: { display: "grid" }, children: [_jsxs(_components.span, { "data-line": "", children: 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style: { color: "#6F42C1" }, children: "stream" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "()" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "map" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(it " }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "->" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: " it" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "parse" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(it))" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "toList" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "();" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: "}" }) }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: " " }) }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: "private" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " Flight" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " parse(" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "String" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " line)" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " var" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " args " }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "=" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: " line" }), _jsx(_components.span, { style: { color: "#212121" }, children: "." }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "split" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "(" }), _jsx(_components.span, { style: { color: "#22863A" }, children: "\",\"" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ");" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " String" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " departure " }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "=" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " args[" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: "0" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "];" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " if" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " (" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "!" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: "isValidIcaoCode(departure)" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ") {" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " throw" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: " new" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: " IllegalArgumentException(" }), _jsx(_components.span, { style: { color: "#22863A" }, children: "\"Departure is not valid ICAO airport code.\"" }), _jsx(_components.span, { style: { color: "#6F42C1" }, children: ")" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: ";" })] }), "\n", _jsx(_components.span, { "data-line": "", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: " }" }) }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " String" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " destination " }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "=" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " args[" }), _jsx(_components.span, { style: { color: "#1976D2" }, children: "1" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: "];" })] }), "\n", _jsxs(_components.span, { "data-line": "", children: [_jsx(_components.span, { style: { color: "#D32F2F" }, children: " if" }), _jsx(_components.span, { style: { color: "#24292EFF" }, children: " (" }), _jsx(_components.span, { style: { color: "#D32F2F" }, children: "!" }), 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Instead of throwing an exception, we just return an object, so the flow is not terminated instantly.\nThe loading part is more problematic because we have to handle ", _jsx(_components.code, { children: "List, Flight>>" }), ".\nThe question is how to aggregate the data to easily display the number of loaded flights or the list of validation errors.\nFor the sake of humanity, there is ", _jsx(_components.code, { children: "Validation#sequence" }), " which:"] }), "\n", _jsxs(_components.blockquote, { children: ["\n", _jsxs(_components.p, { children: ["Reduces many Validation instances into a single Validation by transforming an ", _jsx(_components.code, { children: "Iterable>" }), " into a ", _jsx(_components.code, { children: "Validation>" }), "."] }), "\n"] }), "\n", _jsx(_components.figure, { "data-rehype-pretty-code-figure": "", children: _jsx(_components.pre, { style: { backgroundColor: "#ffffff", color: "#24292eff" }, tabIndex: "0", "data-language": "java", "data-theme": 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"", children: _jsx(_components.span, { style: { color: "#24292EFF" }, children: " }" }) })] }) }) }), "\n", _jsx(References, { links: [{ title: "mixing Mono with Either", url: "https://4programmers.net/Forum/Java/362708-problem_z_mono_w_either?p=1860236#id1860236" }] }), "\n", _jsx(_components.p, { children: "So in Java, I would stick to the basics; otherwise, your colleagues might hate you." }), "\n", _jsx(_components.h2, { id: "summary", children: "Summary" }), "\n", _jsx(_components.p, { children: "We have learned several key concepts of functional programming. These basics are well-supported by the language and should not disturb our team members." }), "\n", _jsxs(_components.ul, { children: ["\n", _jsxs(_components.li, { children: ["Immutability should be our default choice. Use record classes, and the same goes for collections, although you may already be doing this, perhaps unknowingly?\n", _jsx(_components.code, { children: "List.of" }), " returns ", _jsx(_components.code, { children: "ImmutableCollections.List" }), ", ", _jsx(_components.code, { children: "Stream#toList()" }), " returns ", _jsx(_components.code, { children: "Collections.unmodifiableList" }), "."] }), "\n", _jsxs(_components.li, { children: ["For domain errors, prefer ", _jsx(_components.code, { children: "Either" }), " and ", _jsx(_components.code, { children: "Validation" }), ". The latter allows holding a list of errors. Reserve ", _jsx(_components.strong, { children: "exception" }), "s for ", _jsx(_components.strong, { children: "exception" }), "al situations."] }), "\n", _jsxs(_components.li, { children: ["Avoid ", _jsx(_components.code, { children: "void" }), "."] }), "\n"] }), "\n", _jsx(_components.p, { children: "Functional Programming offers us much more, but as Java developers, we can't really apply more advanced concepts to our projects.\nSo, we have to decide if we want to complain about the missing features or live in blissful ignorance." })] }); } function MDXContent(props = {}) { const {wrapper: MDXLayout} = Object.assign({}, _provideComponents(), props.components); return MDXLayout ? _jsx(MDXLayout, Object.assign({}, props, { children: _jsx(_createMdxContent, props) })) : _createMdxContent(props); } return { default: MDXContent }; function _missingMdxReference(id, component) { throw new Error("Expected " + (component ? "component" : "object") + " `" + id + "` to be defined: you likely forgot to import, pass, or provide it."); }

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Toward Functional Paradigm: Fundamental Concepts in Java