Question

这是我的功能签名：

sed '/'[:blank:]'/ c\ NO' inputfile.txt > outputfile.text

以下是我的称呼方式：

export type ReduceCallback<TVal,TAcc> 
    = (accumulator: TAcc, currentValue: TVal, currentIndex: number, array: TVal[]) => TAcc


export function reduceArray<TVal,TAcc>(
    iterable: Iterable<TVal>,
    callback: ReduceCallback<TVal,TAcc>,
    initialValue: TAcc
): TAcc;
export function reduceArray<TVal>(
    iterable: Iterable<TVal>,
    callback: ReduceCallback<TVal,TVal>,
    initialValue?: TVal
): TVal {
    let arr = toArrayStrict(iterable);
    if(initialValue === undefined) {
        return arr.reduce(callback); // 2nd arg has to be fully omitted
    }
    return arr.reduce(callback, initialValue);
}

reduceArray([0,1,2,3], (acc, val) => acc + val)抱怨：

TS2346：提供的参数与呼叫目标的任何签名都不匹配。

但我无法弄清楚原因。我的电话应该匹配第二个功能签名，不是吗？我在通话中省略了tsc，所以它应该别无选择，只能匹配第二个签名。

initialValue是[0,1,2,3]，Iterable<number>应该使用ReduceCallback，这意味着ReduceCallback<number,number>和acc是数字。

有什么问题？

Answer 1

你的重载语法有点不对劲。对于重载，您需要声明每个特定的重载。实际的函数头不算作声明。这意味着在您的情况下，您不幸地必须指定两次函数头：

// because I don't know what toArrayStrict is
declare function toArrayStrict<T>(it: Iterable<T>): T[];

export type ReduceCallback<TVal, TAcc> 
    = (accumulator: TAcc, currentValue: TVal, currentIndex: number, array: TVal[]) => TAcc

export function reduceArray<TVal,TAcc>(
    iterable: Iterable<TVal>,
    callback: ReduceCallback<TVal,TAcc>,
    initialValue: TAcc
): TAcc;
// here we declare the second overload, which is just a duplicate of the actual function header
export function reduceArray<TVal>(
    iterable: Iterable<TVal>,
    callback: ReduceCallback<TVal, TVal>,
    initialValue?: TVal
): TVal;
export function reduceArray<TVal>(
    iterable: Iterable<TVal>,
    callback: ReduceCallback<TVal,TVal>,
    initialValue?: TVal
): TVal {
    let arr = toArrayStrict(iterable);
    if(initialValue === undefined) {
        return arr.reduce(callback); // 2nd arg has to be fully omitted
    }
    return arr.reduce(callback, initialValue);
}

来源：https://www.typescriptlang.org/docs/handbook/functions.html（在底部）

Answer 2

你有两个问题。首先，当你调用reduceArray时，它试图使用第一个重载，因为initialValue是非可选的。其次，您正在寻找的Array.reduce（）的重载具有非可选的第二个参数。

reduce<U>(callbackfn: (previousValue: U, currentValue: T, 
          currentIndex: number, array: ReadonlyArray<T>) => U, initialValue: U): U;

该方法应该自动处理“首次通过”值，因此我简化了该部分。我还将toArrayStrict()替换为Array.from()，因为我无法弄清楚该方法是什么，但它似乎返回了一个数组类型。

export type ReduceCallback<TVal, TAcc> = (accumulator: TAcc, currentValue: TVal, currentIndex: number, array: Array<TVal>) => TAcc

export function reduceArray<TVal, TAcc>(
           iterable: Iterable<TVal>,
           callback: ReduceCallback<TVal, TAcc>,
           initialValue?: TAcc
       ): TAcc;
export function reduceArray<TVal>(
           iterable: Iterable<TVal>,
           callback: ReduceCallback<TVal, TVal>,
           initialValue?: TVal
       ): TVal
{
    let arr = Array.from(iterable);
    return arr.reduce(callback, initialValue);
}

let result = reduceArray([0, 1, 2, 3], (acc: number, val) => acc + val);
console.log(result);

TS2346：提供的参数与调用目标的任何签名都不匹配 - 数组减少函数签名

2 个答案: