Infinities as number literal types

[Andarist]

🔎 Search Terms

infinity number literal

🕗 Version & Regression Information

• This changed in PR Disallow numeric literals with negative numbers #55268

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.3.0-dev.20231031#code/C4TwDgpgBACg9gZwJbCQNwgSQHYDMnYohQC8UAjBAJw0DcAUAPSNSsB6A-PaJFAHIQA5gENUGHPkKhSUALSUaVBs1ZRO9IA

💻 Code

type PositiveInfinity = 1e999;
//   ^?
type NegativeInfinity = -1e999;
//   ^?

🙁 Actual behavior

In TS 5.2 we get NumberLiteralTypes with Infinity and -Infinity values.

In the upcoming TS 5.3 we get a number type in the of the PositiveInfinity

🙂 Expected behavior

I don't know. I created this issue to discuss exactly that.

Should this part of the change be reverted and should Infinity be allowed as a literal number value? Or should -Infinity be aligned with Infinity and should it be converted~ to a number type as well?

Additional information about the issue

I didn't see an Infinity as a literal type so I made this change while working in this area. @rbuckton commented here:

I really hope no one is relying on this.

but it turns out that some try to rely on this. We can see it in this issue, cc @Max10240

[jcalz]

Cross-linking #32277 and #31752

[weswigham]

Also see the original PR and my original PR. My first version had NaN and Infinity types - they're not hard to add if you implement them as compiler internal symbols - @ahejlsberg wanted the compelling usecases for them enumerated before we'd add them, though. Not sure anyone's going to be happy if the only usecase is arithmetic in the typesystem...

[fatcerberus]

Not sure anyone's going to be happy if the only usecase is arithmetic in the typesystem...

Or negated types. number & !NaN, etc.

[ExE-Boss]

Also cross‑linking: #28682, #42905, and #51741

[kevinbarabash]

I'm writing a library that solves algebraic equations and wanted to use Infinity in a enum to model the number of solutions to a linear equation, e.g.

type NumberOfSolutions =  0 | 1 | Infinity;

I can work around this limitation but creating an enum, but being able to use Infinity as a type literal seemed like an elegant way to model the problem.

[ExE-Boss]

@kevinbarabash
For your case, you can replace Infinity with 1e1_000_000 which becomes Infinity in the type system, but you’ll run into #42905 if you emit .d.ts files.