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typescript - Typescript 可选类型推断

问题描述

不确定问题是否正确，但我希望它推断结果类型但实际上不知道如何去做。

我现在是怎么做的：

type StateSetter<S> = (prevState: S) => S;
type ResolvableHookState<S> = S | StateSetter<S>;

export function resolveHookState<S>(state: S): S;
export function resolveHookState<S>(state: StateSetter<S>, currentState?: S): S;
export function resolveHookState<S>(state: ResolvableHookState<S>, currentState?: S): S {
  if (typeof state === 'function') {
    return (state as StateSetter<S>)(currentState as S);
  }

  return state;
}

这是我想使用它的方式：

function someFunction(initialState: ResolvableHookState<number> = 0){
  const resolvedState = resolveHookState(initialState);
}

想法是resolveHookState(initialState)返回数字类型，但由于显而易见的原因它返回ResolvableHookState<number>

我试图通过推断来做到这一点，但它似乎没有像我预期的那样工作。

type ResolvableHookStateType<S extends ResolvableHookState<any>> = S extends StateSetter<infer T> ? T : S;

[UPD 1]
经过一番修修补补，结果如下：

export type StateSetter<S> = (prevState?: S) => S;

export type ResolvableHookState<S> = S | StateSetter<S>;

type ResolvableHookStateType<S> = S extends ResolvableHookState<infer T> ? T : never;

export function resolveHookState<S>(state: S): ResolvableHookStateType<S>;
export function resolveHookState<S>(state: StateSetter<S>, currentState?: S): ResolvableHookStateType<S>;
export function resolveHookState<S>(state: ResolvableHookState<S>, currentState?: S): ResolvableHookStateType<S> {
  if (typeof state === 'function') {
    return (state as StateSetter<S>)(currentState) as ResolvableHookStateType<S>;
  }

  return state as ResolvableHookStateType<S>;

但我不确定这是解决问题的最优雅的方法。

标签： typescripttypescript-generics

解决方案

interface Callable<ReturnType> {
  (...args: any[]): ReturnType;
}

type GenericReturnType<ReturnType, F> = F extends Callable<ReturnType>
  ? ReturnType
  : never;

function someFunction(initialState: ResolvableHookState<number> = 0){
  const resolvedState = GenericReturnType<number, typeof initialState>;
}

这篇文章或许能帮到你。

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