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src/compose.ts
61 строка
2 KB
Mark Erikson
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30 май 2021, 03:37
30 май 2021, 03:37
312a170
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type Func<T extends any[], R> = (...a: T) => R /** * Composes single-argument functions from right to left. The rightmost * function can take multiple arguments as it provides the signature for the * resulting composite function. * * @param funcs The functions to compose. * @returns A function obtained by composing the argument functions from right * to left. For example, `compose(f, g, h)` is identical to doing * `(...args) => f(g(h(...args)))`. */ export default function compose(): <R>(a: R) => R export default function compose<F extends Function>(f: F): F /* two functions */ export default function compose<A, T extends any[], R>( f1: (a: A) => R, f2: Func<T, A> ): Func<T, R> /* three functions */ export default function compose<A, B, T extends any[], R>( f1: (b: B) => R, f2: (a: A) => B, f3: Func<T, A> ): Func<T, R> /* four functions */ export default function compose<A, B, C, T extends any[], R>( f1: (c: C) => R, f2: (b: B) => C, f3: (a: A) => B, f4: Func<T, A> ): Func<T, R> /* rest */ export default function compose<R>( f1: (a: any) => R, ...funcs: Function[] ): (...args: any[]) => R export default function compose<R>(...funcs: Function[]): (...args: any[]) => R export default function compose(...funcs: Function[]) { if (funcs.length === 0) { // infer the argument type so it is usable in inference down the line return <T>(arg: T) => arg } if (funcs.length === 1) { return funcs[0] } return funcs.reduce( (a, b) => (...args: any) => a(b(...args)) ) }