TypeScript 模板文字类型 - 如何推断数字类型？

Question

// from a library
type T = null | "auto" | "text0" | "text1" | "text2" | "text3" | "text4";

//in my code
type N = Extract<T, `text${number}`> extends `text${infer R}` ? R : never

(TS playground)

上面的代码 N 等价于 "0" | "1" | "2" | "3" | "4"。如何将其转换为数字类型，即 0 | 1 | 2 | 3 | 4？已经尝试将 & number 放在某些地方，例如 infer R & number，但是 none 有效。

Answer 1

更新

type MAXIMUM_ALLOWED_BOUNDARY = 999

type Mapped<
    N extends number,
    Result extends Array<unknown> = [],
    > =
    (Result['length'] extends N
        ? Result
        : Mapped<N, [...Result, Result['length']]>
    )


type NumberRange = Mapped<MAXIMUM_ALLOWED_BOUNDARY>[number] // 0.. 998


type ConvertToNumber<T extends string, Range extends number> =
    (Range extends any
        ? (`${Range}` extends T
            ? Range
            : never)
        : never)

type _ = ConvertToNumber<'5', NumberRange> // 5
type __ = ConvertToNumber<'125', NumberRange> // 125

Playground

P.S。不好意思命名，我不擅长。

目前看来这是不可能的，但有一个解决方法。

您可以为 0..42:

范围内的数字创建 Dictionary

// from a library
type Texts<T extends PropertyKey> = T extends number ? `text${T}` : never

type T = null | "auto" | Texts<Enumerate<43>>;

type PrependNextNum<A extends Array<unknown>> = A['length'] extends infer T ? ((t: T, ...a: A) => void) extends ((...x: infer X) => void) ? X : never : never;

type EnumerateInternal<A extends Array<unknown>, N extends number> = { 0: A, 1: EnumerateInternal<PrependNextNum<A>, N> }[N extends A['length'] ? 0 : 1];

type Enumerate<N extends number> = EnumerateInternal<[], N> extends (infer E)[] ? E : never;

type Dictionary = {
    [Prop in Enumerate<43> as `${Prop}`]: Prop
}

//  0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 ... 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42
type N =
    Extract<T, `text${number}`> extends `text${infer R}`
    ? R extends keyof Dictionary
    ? Dictionary[R]
    : never
    : never

合并Tail recursion PR后可能会产生更长的距离

Playground

更新 - 就像我承诺的那样

尝试

type MAXIMUM_ALLOWED_BOUNDARY = 999

type Mapped<
    N extends number,
    Result extends Array<unknown> = [],
    > =
    (Result['length'] extends N
        ? Result
        : Mapped<N, [...Result, Result['length']]>
    )

// 0 , 1, 2 ... 998
type NumberRange = Mapped<MAXIMUM_ALLOWED_BOUNDARY>[number]


type Texts<T extends PropertyKey> = T extends number ? `text${T}` : never


type T = null | "auto" | Texts<NumberRange>;

type Dictionary = {
    [Prop in NumberRange as `${Prop}`]: Prop
}

//  0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 ... 998
type N =
    Extract<T, `text${number}`> extends `text${infer R}`
    ? R extends keyof Dictionary
    ? Dictionary[R]
    : never
    : never

Playground

您可以在 TS playground 中使用 TS 版本 4.5（每晚）尝试上述解决方案代码就简单多了。

这里有 javascript 代表 Mapped:

const Mapped = (N: number, Result: number[] = []): number[] => {
    if (Result.length === N) {
        return Result
    }
    return Mapped(N, [...Result, Result.length])
}

没什么复杂的。尾递归。

Answer 2

感谢@captain-yossarian 的回答。我发现您还可以使用字符串索引保留 Mapped<MAXIMUM_ALLOWED_BOUNDARY> 和索引的元组。当然，Range必须是一个元组。

type MAXIMUM_ALLOWED_BOUNDARY = 999

type Mapped<
    N extends number,
    Result extends Array<unknown> = [],
    > =
    (Result['length'] extends N
        ? Result
        : Mapped<N, [...Result, Result['length']]>
    )


type NumberRange = Mapped<MAXIMUM_ALLOWED_BOUNDARY>; // <- tuple [0, 1, 2, 3, ...]


type ConvertToNumber<T extends string, Range extends number[]> = 
  T extends keyof Range ? Range[T] : never;

type _ = ConvertToNumber<'5', NumberRange> // 5
type __ = ConvertToNumber<'125', NumberRange> // 125

Playground

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