[SOLVED] Why is it that this function returns the literal type and making the return value type a tuple returns a general type?

Issue

I have a function that takes one argument and returns it as it is:

function test<T>(input: T): T {
    return input
}

I found that if I pass a number or string, the returned type is going to be a literal type


const res = test(1) // 1
const input = 1
const res2 = test(input) // 1

But if I slightly change the function to make it return a tuple:

function test2<T>(input: T): [T] {
    return [input]
}

then the return type becomes just the string or number type:

const res3 = test2(1) // [number]

So here I have two questions:

Why does the test function return literal types? Are there any resources I can read to learn this behaviour?
Why is it that wrapping the return value into a tuple solves this?

why is the test function returns literal types? Are there any resources I can read to learn this behaviour?

TypeScript infers primitive types. You can read about function parameter type inference here:

why is that wrapping the return value into a tuple solves this?

Answered By – jsejcksn