type Type = {
  key: "value"
}
interface Interface {
  key: "value"
}

type 似乎沒差別都是true = Type extends Interface ? Type extends Interface ? true : false : false

type 坑點(diǎn) = {
  [key: string]: 坑點(diǎn)
} | string

type 測(cè)試<T> = T extends 坑點(diǎn) ? true : false
type 這個(gè)是true = 測(cè)試<Type>
type 這個(gè)是false = 測(cè)試<Interface>

//差不多這意思，下面的代碼懶得實(shí)際測(cè)了🙃

//fns是個(gè)函數(shù)索引表，TFns是索引表的const類型
function 重載失敗<T extends keyof TFns>(fn:T, params: Parameters<fns[T]>){
    fns[fn](...params)//在實(shí)現(xiàn)中聯(lián)合類型不會(huì)縮小，所以會(huì)報(bào)錯(cuò)
    //錯(cuò)誤應(yīng)該像是 不能將方法1的參數(shù)傳給方法2 這種
}
//但外部使用時(shí)，符合類型的語義也沒啥事

//需要的類型：[...number[], "middle-element", ...boolean[]] 
//上面的寫法是無效的，只是示意下面的類型代碼是干什么用的（實(shí)現(xiàn)上面示意的類型約束）

type Elem = number | boolean | "middle-element";

type Last<T extends any[]> = T extends [infer _]
  ? never
  : T extends [...infer _, infer Tl]
  ? Tl
  : never

type HandleEmpty<T extends any[], Data> = T['length'] extends 0 ? never : Data

type Validation<Params extends any[], Cache extends Elem[] = []> =
  Params extends []
  ? Cache['length'] extends 0
  ? never
  : Cache
  : Params extends [infer Fst, ...infer Rest]
  ? Cache extends []
  ? Fst extends number
  ? HandleEmpty<Rest, Validation<Rest, [...Cache, Fst]>>
  : never
  : Fst extends number
  ? Last<Cache> extends number
  ? HandleEmpty<Rest, Validation<Rest, [...Cache, Fst]>>
  : never
  : Fst extends "middle-element"
  ? Last<Cache> extends number
  ? HandleEmpty<Rest, Validation<Rest, [...Cache, Fst]>>
  : never
  : "middle-element" extends Cache[number]
  ? Fst extends boolean
  ? Validation<Rest, [...Cache, Fst]>
  : never
  : never
  : never

type IsNever<T> = [T] extends [never] ? true : false;

function check<
  Params extends Elem[],
  IsValid extends Validation<Params>
>(...arr: IsNever<IsValid> extends true ? [never] : [...Params]) {
  return arr
}

const 正常 = check(1, 'middle-element', false)
const 報(bào)錯(cuò) = check(false, "middle-element", 2)

//{ "new-a":any; "new-b":any }
type 重映射 = {
    [K in "a" | "b" as `new-${K}`]: any
}

//"a1"|"b2"
type 拆分成功<_Keys = keyof { a: 1, b: 2 }> = _Keys extends infer K ?
    `${Extract<K, string>}${{ a: 1, b: 2 }[Extract<K, _Keys>]}`
    : never

//注意：（截止ts4.4.4）直接`keyof Obj extends infer K`無法分割聯(lián)合類型，原因不明（懶得查😁）。
//結(jié)果是"a1"|"a2"|"b1"|"b2"
type 拆分失敗 = keyof { a: 1, b: 2 } extends infer K ?
    `${Extract<K, string>}${{ a: 1, b: 2 }[Extract<K, "a" | "b">]}`
    : never

type 轉(zhuǎn)換器<T> = T extends string ? "str" : null
//進(jìn)去是個(gè)[string,number,string]，出來就會(huì)是["str",null,"str"]
type 遞歸<
        輸入源 extends any[],
        內(nèi)部的類型緩存 extends any[] = []
    > = 輸入源 extends [any, ...infer 剩余元素] ?
        遞歸<剩余元素, [...內(nèi)部的類型緩存, 轉(zhuǎn)換器<輸入源[0]>]>
        : 輸入源