Array.length type guard for array spreading

TypeScript Version: 3.3.0-dev.20181204

Search Terms: array length type guard spread

Code

const timeString = '09:00';
const date = new Date();
const timeParts = timeString.split(':').map((part) => parseInt(part, 10));
if (timeParts.length > 0) {
    date.setHours(...timeParts);
}

Expected behavior: No errors

Actual behavior: TS2556: Expected 1-4 arguments, but got 0 or more.

Playground Link: https://www.typescriptlang.org/play/#src=const timeString %3D ‘09%3A00’%3B const date %3D new Date()%3B const timeParts %3D timeString.split(‘%3A’).map((part) %3D> parseInt(part%2C 10))%3B%0D%0Aif%20(timeParts.length%20%3E%200)%20%7B%0D%0A%20%20%20%20date.setHours(…timeParts)%3B%0D%0A%7D%0D%0A

Related Issues: None

[zheeeng]

I have the same request:

I want a convenient and easy-to-maintain way to support the future branches-exploding.

function fn0(a: any) { 
    return a
}
function fn1(a: any, b: any) {
    return a
}
function fn2(a: any, b: any, c: any) {
    return a
}
function fn3(a: any, b: any, c: any, d: any) {
    return a
}
function fn4(a: any, b: any, c: any, d: any, e: any) {
    return a
}

function fn(...args: any[]) {
    switch (args.length) {
        case 1:
            return fn0(args[0])
        case 2:
            return fn1(args[0], args[1])
        case 3:
            return fn2(args[0], args[1], args[2])
        case 4:
            return fn3(args[0], args[1], args[2], args[3])
        case 5:
            return fn4(args[0], args[1], args[2], args[3], args[4])
        default:
            throw Error()
    }
}

I expect to refactor fn to the below way:

function fn(...args: any[]) {
    switch (args.length) {
        case 1:
            //Expected 1 arguments, but got 0 or more.
            return fn0(...args)
        case 2:
            return fn1(...args)
        case 3:
            return fn2(...args)
        case 4:
            return fn3(...args)
        case 5:
            return fn4(...args)
        default:
            throw Error()
    }
}

[weswigham]

More like “we’re waiting for more people to weigh in before we take decisive action in any direction”