TypeScript Equal custom type All In One

TypeScript Equal custom type All In One

Equal

import type { Equal, Expect } from '@type-challenges/utils'

// (alias) type Equal<X, Y> = (<T>() => T extends X ? 1 : 2) extends <T>() => T extends Y ? 1 : 2 ? true : false

demos

type GetReadonlyKeys<T> = keyof {[Key in keyof T as Equal<Pick<T, Key>, Readonly<Pick<T, Key>>> extends true ? Key : never]: Key}

/*
5 - 获取只读字段

#地狱 #utils #object-keys

### 题目

实现泛型`GetReadonlyKeys<T>`，`GetReadonlyKeys<T>`返回由对象 T 所有 只读属性 的键组成的 联合类型。

例如

/`/`/`ts
  interface Todo {
    readonly title: string
    readonly description: string
    completed: boolean
  }

  type Keys = GetReadonlyKeys<Todo> // expected to be "title" | "description"
/`/`/`

*/

// type GetReadonlyKeys<T> = any;

type GetReadonlyKeys<T> = keyof {[Key in keyof T as Equal<Pick<T, Key>, Readonly<Pick<T, Key>>> extends true ? Key : never]: Key}



// 测试用例

import type { Equal, Expect } from '@type-challenges/utils'

// (alias) type Equal<X, Y> = (<T>() => T extends X ? 1 : 2) extends <T>() => T extends Y ? 1 : 2 ? true : false


interface Todo1 {
  readonly title: string
  description: string
  completed: boolean
}

interface Todo2 {
  readonly title: string
  readonly description: string
  completed?: boolean
}

type cases = [
  Expect<Equal<'title', GetReadonlyKeys<Todo1>>>,
  Expect<Equal<'title' | 'description', GetReadonlyKeys<Todo2>>>,
]

https://www.typescriptlang.org/play

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refs

https://github.com/xgqfrms/developer-mind-mapping/blob/main/todos/chrome-tabs.md#typescript

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