A range of numbers

[DanMossa]

Something built in like this
https://stackoverflow.com/questions/39494689/is-it-possible-to-restrict-number-to-a-certain-range

Instead of

interface Car {
  model: string,
  year: 1999|2000|2001|2002
}

It would be nice to be able to do

interface Car {
  model: string,
  year: NumberRange<1999, 2002>
}

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[sindresorhus]

I think we could do something like what's done here: microsoft/TypeScript#15480 (comment) (don't forget to 👍🏻 on that issue) But it would be limited to a range of 40. That should be enough for many use-cases though.

[henryruhs]

What about this, stolen from stackoverflow and modified to work properly:

type Enumerate<NUMBER extends number, ARRAY extends number[] = []> = ARRAY['length'] extends NUMBER
    ? ARRAY[number] : Enumerate<NUMBER, [ ...ARRAY, ARRAY['length'] ]>
export type Range<FROM extends number, TO extends number> = Exclude<Enumerate<TO>, Enumerate<FROM>> | TO;

Some testing:

const validOne: Range<0, 100> = 0;
const validTwo: Range<0, 100> = 100;
const invalidOne: Range<0, 100> = 101;
const invalidTwo: Range<0, 100> = -1;

// my IDE show a warning as of the recursive call
const invalidThree: Range<0, 1000> = 1001;

[sindresorhus]

Seems like it's now possible with TypeScript 4.8: https://twitter.com/anuraghazru/status/1573328100246822917

Nice work, @anuraghazra

[souporserious]

I came across this problem on reddit and then checked this library to see if there was a utility yet. Not sure if this can be expanded further, but it seems there's a way to bypass the excessive iterations error after 1000 using template literals, see here.

[tommy-mitchell]

I’ve started working on implementing a solution similar to microsoft/TypeScript#15480 (comment), with options to control the step size, if the range is inclusive, and if the range should be a union instead of a tuple (using UnionToTuple). Should the name be Range, as in Range<Start, End, Options>?

Still trying to figure out how to infer End if only Start is set:

type FiveNumbers = Range<5>;
//=> [0, 1, 2, 3, 4]

I also think it would be worth adding a RangeUnion wrapper that is just a Range with the {asUnion: true} option set. It should probably be inclusive as well, as that seems to be a common use for the union type.

[sindresorhus]

Should the name be Range, as in Range<Start, End, Options>?

👍

[jd-solanki]

Another solution: https://stackoverflow.com/a/39495173/10796681