「重学TS 2.0 」TS 练习题第九题 about awesome-typescript HOT 26 OPEN

type JoinStrArray<
  Arr extends string[],
  Separator extends string
> = Arr extends [infer A, ...infer B]
  ? `${A extends string ? A : ''}${B extends [string, ...string[]]
      ? `${Separator}${JoinStrArray<B, Separator>}`
      : ''}`
  : '';

// 定义一个 JoinStrArray 工具类型，用于根据指定的 Separator 分隔符，对字符串数组类型进行拼接。具体的使用示例如下所示：

type JoinStrArray<Arr extends string[], Separator extends string, Result extends string = ""> = Arr extends [infer A, ...infer B]
  ? Result extends ""
    ? JoinStrArray<B, Separator, A>
    : JoinStrArray<B, Separator, `${Result}${Separator}${A}`>
  : Result;

// 测试用例
type Names = ["Sem", "Lolo", "Kaquko"]
type NamesComma = JoinStrArray<Names, ","> // "Sem,Lolo,Kaquko"
type NamesSpace = JoinStrArray<Names, " "> // "Sem Lolo Kaquko"
type NamesStars = JoinStrArray<Names, "⭐️"> // "Sem⭐️Lolo⭐️Kaquko"

type JoinStrArray<Arr extends string[], Separator extends string, Result extends string = ""> = 
    Arr extends [infer El,...infer Rest] ? 
            Rest extends string[] ?
            El extends string ?
            Result extends "" ?
            JoinStrArray<Rest, Separator,`${El}`> :
            JoinStrArray<Rest, Separator,`${Result}${Separator}${El}`> :
            `${Result}` :
            `${Result}` :
            `${Result}`

type Names = ["Sem", "Lolo", "Kaquko"]
type NamesComma = JoinStrArray<Names, ","> // "Sem,Lolo,Kaquko"
type NamesSpace = JoinStrArray<Names, " "> // "Sem Lolo Kaquko"
type NamesStars = JoinStrArray<Names, "⭐️"> // "Sem⭐️Lolo⭐️Kaquko"

type JoinStrArray<Arr extends string[], Separator extends string> = Arr extends [infer El, ...infer Res]
    ? `${Arr[0]}${Res extends string[]
        ? Res[0] extends string
            ? `${Separator}${JoinStrArray<Res, Separator>}`
            : ""
        : ""}`
    : ""

// 测试用例
type Names = ["Sem", "Lolo", "Kaquko"]
type NamesComma = JoinStrArray<Names, ","> // "Sem,Lolo,Kaquko"
type NamesSpace = JoinStrArray<Names, " "> // "Sem Lolo Kaquko"
type NamesStars = JoinStrArray<Names, "⭐️"> // "Sem⭐️Lolo⭐️Kaquko"

type JoinStrArray<Arr extends string[], Separator extends string, Result extends string = ""> = 
    Arr['length'] extends 0
        ? Result
        : Arr extends [infer First, ...infer Rest]
              ? First extends string
        ? Rest extends string[]
          ? Rest['length'] extends 0
            ? JoinStrArray<Rest, Separator, `${Result}${First}`>
            : JoinStrArray<Rest, Separator, `${Result}${First}${Separator}`>
          : ''
        : ''
      : ''

// 测试用例
type Names = ["Sem", "Lolo", "Kaquko"]
type NamesComma = JoinStrArray<Names, ","> // "Sem,Lolo,Kaquko"
type NamesSpace = JoinStrArray<Names, " "> // "Sem Lolo Kaquko"
type NamesStars = JoinStrArray<Names, "⭐️"> // "Sem⭐️Lolo⭐️Kaquko"

type JoinStrArray<
  Arr extends string[],
  Separator extends string,
  Result extends string = ""
> = Arr extends [infer F, ...infer R]
  ? R extends string[]
    ? F extends string
      ? Result extends ""
        ? JoinStrArray<R, Separator, F>
        : JoinStrArray<R, Separator, `${Result}${Separator}${F}`>
      : Result
    : Result
  : Result;

type JoinStrArray<Arr extends string[], Separator extends string, Result extends string = ""> = 
    Arr extends [infer El,...infer Rest] ? //一层判断，若true则执行第二层判断。否则执行结果1
            Rest extends string[] ?  //二层判断，若true则执行第三层判断。否则执行结果2
            El extends string ?  //三层判断，若true则执行第四层判断。否则执行结果3
            Result extends "" ?  //四层判断，若true则执行结果5。否则执行结果4
            JoinStrArray<Rest, Separator,`${El}`> :  //结果5
            JoinStrArray<Rest, Separator,`${Result}${Separator}${El}`> : //结果4
            `${Result}` :  //结果3
            `${Result}` :  //结果2
            `${Result}`   //结果1

//上面的判断把每组三元表达式画个括号层次就清楚了
//一二三层判断是为了判断递归中是否还有非空数组传进来，有就继续拼接，没有则返回上回拼接结果
//结果5为首次递归，传递数组第一个元素作为拼接结果
//结果4为非首次递归，将当前数组第一个元素和上次拼接结果进行拼接并传递给下回

type Names = ["Sem", "Lolo", "Kaquko"]
type NamesComma = JoinStrArray<Names, ","> // "Sem,Lolo,Kaquko"
type NamesSpace = JoinStrArray<Names, " "> // "Sem Lolo Kaquko"
type NamesStars = JoinStrArray<Names, "⭐️"> // "Sem⭐️Lolo⭐️Kaquko"

type JoinStrArray<Arr extends string[], Separator extends string, Result extends string = ""> = 
    Arr extends [infer El,...infer Rest]
    ? Rest extends string[]
      ? El extends string
        ? Result extends ""
          ? JoinStrArray<Rest, Separator,`${El}`>
          : JoinStrArray<Rest, Separator,`${Result}${Separator}${El}`>
        :`${Result}`
      : `${Result}`
    : `${Result}`

//没看懂那个Result是干嘛的
type JoinStrArray<
	Arr extends string[],
	Separator extends string,
> = Arr extends [infer First extends string, ...infer Rest extends string[]]
	? `${First}${Separator}${JoinStrArray<Rest, Separator>}`
	: "";