TypeScript中类型映射的使用

type A = {
  foo: number;
  bar: number;
};

type B = {
  [prop in keyof A]: string;
};

type A = {
  foo: number;
  bar: string;
};

type B = {
  [prop in keyof A]: A[prop];
};

type ToBoolean<Type> = {
  [Property in keyof Type]: boolean;
};

type MyObj = {
  [p in 'foo']: number;
};

// 等同于
type MyObj = {
  foo: number;
};

type A = {
  a: string;
  b: number;
};

type B = {
  [Prop in keyof A]?: A[Prop];
};

// 将 T 的所有属性改为只读属性
type Readonly<T> = {
  readonly [P in keyof T]: T[P];
};
// 用法如下。
type T = { a: string; b: number };

type ReadonlyT = Readonly<T>;
// {
//   readonly a: string;
//   readonly b: number;
// }

// 添加可选属性
type Optional<Type> = {
  [Prop in keyof Type]+?: Type[Prop];
};

// 移除可选属性
type Concrete<Type> = {
  [Prop in keyof Type]-?: Type[Prop];
};

// 添加 readonly
type CreateImmutable<Type> = {
  +readonly [Prop in keyof Type]: Type[Prop];
};

// 移除 readonly
type CreateMutable<Type> = {
  -readonly [Prop in keyof Type]: Type[Prop];
};

// 增加
type MyObj<T> = {
  +readonly [P in keyof T]+?: T[P];
};

// 移除
type MyObj<T> = {
  -readonly [P in keyof T]-?: T[P];
}

type A = {
  foo: number;
  bar: number;
};

type B = {
  [p in keyof A as `${p}ID`]: number;
};

// 等同于
type B = {
  fooID: number;
  barID: number;
};

type S = {
  kind: 'square',
  x: number,
  y: number,
};

type C = {
  kind: 'circle',
  radius: number,
};

type MyEvents<Events extends { kind: string }> = {
  [E in Events as E['kind']]: (event: E) => void;
}

type Config = MyEvents<S|C>;
// 等同于
type Config = {
  square: (event:S) => void;
  circle: (event:C) => void;
}