TypeScript で compose 関数を入力する

compose 関数のクレイジーで、読めず、保守も不可能なタイピングを書きましょう.多分あなたは新しいことを学ぶでしょう.

いくつかの基本型とユーティリティを定義しましょう.

type Fn = (a: any) => any

type Head<T extends any[]> =
    T extends [infer H, ...infer _]
    ? H
    : never;

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

type Foo = typeof foo
type Bar = typeof bar
type Baz = typeof baz

私たちの主な目標は、引数の長さの制限なしで compose を作成することです.

たとえば、lodash の構成タイピングを見てみましょう.

    interface LodashFlowRight {
        <A extends any[], R1, R2, R3, R4, R5, R6, R7>(f7: (a: R6) => R7, f6: (a: R5) => R6, f5: (a: R4) => R5, f4: (a: R3) => R4, f3: (a: R2) => R3, f2: (a: R1) => R2, f1: (...args: A) => R1): (...args: A) => R7;
        <A extends any[], R1, R2, R3, R4, R5, R6>(f6: (a: R5) => R6, f5: (a: R4) => R5, f4: (a: R3) => R4, f3: (a: R2) => R3, f2: (a: R1) => R2, f1: (...args: A) => R1): (...args: A) => R6;
        <A extends any[], R1, R2, R3, R4, R5>(f5: (a: R4) => R5, f4: (a: R3) => R4, f3: (a: R2) => R3, f2: (a: R1) => R2, f1: (...args: A) => R1): (...args: A) => R5;
        <A extends any[], R1, R2, R3, R4>(f4: (a: R3) => R4, f3: (a: R2) => R3, f2: (a: R1) => R2, f1: (...args: A) => R1): (...args: A) => R4;
        <A extends any[], R1, R2, R3>(f3: (a: R2) => R3, f2: (a: R1) => R2, f1: (...args: A) => R1): (...args: A) => R3;
        <A extends any[], R1, R2>(f2: (a: R1) => R2, f1: (...args: A) => R1): (...args: A) => R2;
        (...func: Array<lodash.Many<(...args: any[]) => any>>): (...args: any[]) => any;
    }

引数には制限があります.

制限なし、少なくとも明示的な制限なしで関数を書いてみましょう. TS には独自の再帰制限があることに注意してください.

検証ロジックから始めます.

type Allowed<
    T extends Fn[],
    Cache extends Fn[] = []
    > =
    T extends []
    ? Cache
    : T extends [infer Lst]
    ? Lst extends Fn
    ? Allowed<[], [...Cache, Lst]> : never
    : T extends [infer Fst, ...infer Lst]
    ? Fst extends Fn
    ? Lst extends Fn[]
    ? Head<Lst> extends Fn
    ? Head<Parameters<Fst>> extends ReturnType<Head<Lst>>
    ? Allowed<Lst, [...Cache, Fst]>
    : never
    : never
    : never
    : never
    : never;

上記の型は、配列内のすべての関数を反復し、現在の関数の引数が次の関数の戻り型に割り当て可能かどうかを確認します Head<Parameters<Fst>> extends ReturnType<Head<Lst>>
次に、単純なヘルパーを定義できます.

type LastParameterOf<T extends Fn[]> =
    Last<T> extends Fn
    ? Head<Parameters<Last<T>>>
    : never

type Return<T extends Fn[]> =
    Head<T> extends Fn
    ? ReturnType<Head<T>>
    : never

最後に、compose 関数:

function compose<T extends Fn, Fns extends T[], Allow extends {
    0: [never],
    1: [LastParameterOf<Fns>]
}[Allowed<Fns> extends never ? 0 : 1]>
    (...args: [...Fns]): (...data: Allow) => Return<Fns>

function compose<
    T extends Fn,
    Fns extends T[], Allow extends unknown[]
>(...args: [...Fns]) {
    return (...data: Allow) =>
        args.reduceRight((acc, elem) => elem(acc), data)
}

お気づきかもしれませんが、ここではオーバーロードを 1 つしか定義していません.これは悪い習慣と考えられています.常に少なくとも 2 つ定義する必要があります.そのために残念.

コピー/貼り付けの完全な例:

type Foo = typeof foo
type Bar = typeof bar
type Baz = typeof baz


type Fn = (a: any) => any

type Head<T extends any[]> =
    T extends [infer H, ...infer _]
    ? H
    : never;

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


type Allowed<
    T extends Fn[],
    Cache extends Fn[] = []
    > =
    T extends []
    ? Cache
    : T extends [infer Lst]
    ? Lst extends Fn
    ? Allowed<[], [...Cache, Lst]> : never
    : T extends [infer Fst, ...infer Lst]
    ? Fst extends Fn
    ? Lst extends Fn[]
    ? Head<Lst> extends Fn
    ? Head<Parameters<Fst>> extends ReturnType<Head<Lst>>
    ? Allowed<Lst, [...Cache, Fst]>
    : never
    : never
    : never
    : never
    : never;

type LastParameterOf<T extends Fn[]> =
    Last<T> extends Fn
    ? Head<Parameters<Last<T>>>
    : never

type Return<T extends Fn[]> =
    Head<T> extends Fn
    ? ReturnType<Head<T>>
    : never


function compose<T extends Fn, Fns extends T[], Allow extends {
    0: [never],
    1: [LastParameterOf<Fns>]
}[Allowed<Fns> extends never ? 0 : 1]>
    (...args: [...Fns]): (...data: Allow) => Return<Fns>

function compose<
    T extends Fn,
    Fns extends T[], Allow extends unknown[]
>(...args: [...Fns]) {
    return (...data: Allow) =>
        args.reduceRight((acc, elem) => elem(acc), data)
}

const foo = (arg: 1 | 2) => [1, 2, 3]
const bar = (arg: string) => arg.length > 10 ? 1 : 2
const baz = (arg: number[]) => 'hello'

const check = compose(foo, bar, baz)([1, 2, 3]) // [number]
const check2 = compose(bar, foo)(1) // expected error