بناء الاتحادات المميّزة

ما الاتحاد المميّز؟

// The shared "kind" property is the discriminant
type Circle = { kind: "circle"; radius: number };
type Square = { kind: "square"; side: number };
type Shape = Circle | Square;

الخاصية المميّزة

type Circle = { kind: "circle"; radius: number };
type Square = { kind: "square"; side: number };

const c: Circle = { kind: "circle", radius: 10 };
console.log(c.kind); // "circle"

لكل عضو حقوله الخاصة

type Circle = { kind: "circle"; radius: number };
type Square = { kind: "square"; side: number };
type Rectangle = { kind: "rectangle"; width: number; height: number };
type Shape = Circle | Square | Rectangle;

إنشاء قيم الاتحاد

type Shape =
  | { kind: "circle"; radius: number }
  | { kind: "square"; side: number };

const shapes: Shape[] = [
  { kind: "circle", radius: 5 },
  { kind: "square", side: 4 }
];
console.log(shapes.length); // 2

لماذا لا نستخدم الحقول الاختيارية فقط؟

// Loose and error-prone: nothing stops radius + side together
type BadShape = { radius?: number; side?: number };
const bad: BadShape = { radius: 5, side: 4 }; // nonsense, but allowed

اسم الخاصية المميّزة متروك لك

type Event =
  | { type: "click"; x: number; y: number }
  | { type: "scroll"; delta: number };

const e: Event = { type: "click", x: 10, y: 20 };
console.log(e.type); // "click"

نمذجة حاسبة مساحة الأشكال

type Shape =
  | { kind: "circle"; radius: number }
  | { kind: "square"; side: number };

const myShapes: Shape[] = [
  { kind: "circle", radius: 3 },
  { kind: "square", side: 6 }
];
console.log("Count:", myShapes.length);

إضافة نوع مختلف ثالث

type Shape =
  | { kind: "circle"; radius: number }
  | { kind: "square"; side: number }
  | { kind: "triangle"; base: number; height: number };

const t: Shape = { kind: "triangle", base: 4, height: 8 };
console.log(t.kind);

القيم الحرفية الفريدة تمنع التداخل

type A = { kind: "a"; value: number };
type B = { kind: "b"; label: string };
type Union = A | B;

function describe(u: Union) {
  return u.kind === "a" ? u.value : u.label;
}
console.log(describe({ kind: "b", label: "hi" }));

الخصائص المميّزة ذات العلامات المنطقية

type Result =
  | { ok: true; data: string }
  | { ok: false; error: string };

const r: Result = { ok: true, data: "loaded" };
console.log(r.ok ? r.data : r.error);

الاتحادات المميّزة عمليًا

type Shape =
  | { kind: "circle"; radius: number }
  | { kind: "square"; side: number };

const sample: Shape = { kind: "circle", radius: 7 };
console.log(sample.kind, "ready");

تحقق سريع: الخصائص المميّزة

مراجعة: إنشاء الاتحادات المميّزة

type Shape =
  | { kind: "circle"; radius: number }
  | { kind: "square"; side: number };

const done: Shape = { kind: "square", side: 2 };
console.log("Recap complete:", done.kind);