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TypeScript - 联合类型的typeof数组

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如果我有一个联合数组，我可以这样检查typeof值：

//case 1
function something1(a1: Array<number | string | boolean>)
{
    for (const v of a1)
        if (typeof v === "number")
            v;  //v is number
        else if (typeof v === "boolean")
            v;  //v is boolean
        else
            v;  //v is string
}

如果我有数组联合，我可以这样做：

//case 2
function something2(a1: Array<number> | Array<string> | Array<boolean>)
{
    for (const v of a1)
        if (typeof v === "number")
            v;  //v is number
        else if (typeof v === "boolean")
            v;  //v is boolean
        else
            v;  //v is string
}

但我想避免检查内部循环类型：

//case 3
function something3(a1: Array<number> | Array<string> | Array<boolean>)
{
    if (a1.length === 0)
        return;
    if (typeof a1[0] === "number")
        a1;  //should be number[]!!     but it is  number[] | string[] | boolean[]
    if (typeof a1[0] === "boolean")
        a1;  //should be boolean[]!!    but it is  number[] | string[] | boolean[]
    if (typeof a1[0] === "string")
        a1;  //should be string[]!!     but it is  number[] | string[] | boolean[]
}

但是a1不被识别为number []或string []或boolean [] .
但这是有道理的 . 由于数组中的所有项都是相同的类型 . 是否有可能实现这一目标？

我正在使用TypeScript beta 2.0 .

typescript

1 回答

  • 3

    使用type guards：

    function something3(a1: Array<number> | Array<string> | Array<boolean>) {
    if (a1.length === 0)
        return;
    if (isArrayOfNumbers(a1))
        a1[0].toExponential();
    if (isArrayOfBooleans(a1))
        a1[0].valueOf();
    if (isArrayOfStrings(a1))
        a1[0].indexOf('abc');
}

function isArrayOfNumbers(arr: number[] | string[] | boolean[]) : arr is number[] {
    return arr.length > 0 && typeof arr[0] === 'number';
}

function isArrayOfBooleans(arr: number[] | string[] | boolean[]) : arr is boolean[] {
    return arr.length > 0 && typeof arr[0] === 'boolean';
}

function isArrayOfStrings(arr: number[] | string[] | boolean[]) : arr is string[] {
    return arr.length > 0 && typeof arr[0] === 'string';
}
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