Святослав Хусамов

This is a bit subtle, but number[] | string[] !=== (number | string)[]. The first one has an assert on homogeneity, while the second does not. just as in the example noted above by @kaotik4266, [0, "1", 2] is not of type number[] | string[].

There is not a meaningful way to describe the general case for merging unmatching signatures; while filter might be arguably safe, push is not. So merging the signatures of (number[]|string[]).push(...) th same proposed for filter would result in push(a: number | string); which means that we are treating the original type as (number | string)[], which is not type safe.

So the general case, is there is no common signatures between the two types, and thus the resulting union type does have a filter property but it does not have a signature, and hence the error message Cannot invoke an expression whose type lacks a call signature.

function isNumbers(arr: number[] | string[]): arr is number[] {
    return arr.length === 0 || // В случае нулевой длины тип элемента массива нам не важен, примем его за number
        typeof arr[0] === "number"; // Либо проверим фактический тип первого элемента. Этого должно быть
            // достаточно, т.к. в типе 'arr' декларируется однородность массивов
}

function getHandler(handlers: number[] | string[]): number[] | string[] {
    if (isNumbers(handlers)) {
        return handlers.map(handler => handler);
    } else {
        return handlers.map(handler => handler);
    }
}

[paths]
default = https://username@bitbucket.org/repository/path

[auth]
bb.prefix = https://bitbucket.org/repository/path
bb.username = username
bb.password = password

interface ClockConstructor {
    new (hour: number, minute: number): ClockInterface;
}
interface ClockInterface {
    tick();
}

function createClock(ctor: ClockConstructor, hour: number, minute: number): ClockInterface {
    return new ctor(hour, minute);
}

class DigitalClock implements ClockInterface {
    constructor(h: number, m: number) { }
    tick() {
        console.log("beep beep");
    }
}
class AnalogClock implements ClockInterface {
    constructor(h: number, m: number) { }
    tick() {
        console.log("tick tock");
    }
}

let digital = createClock(DigitalClock, 12, 17);
let analog = createClock(AnalogClock, 7, 32);

dir ^
/ad ^
c:\temp