Improve `is.integer`, `is.safeInteger`, `is.infinite` TypeScript type

[younho9]

• It requires typescript@4.1.2, since Integer type in type-fest is using template literal type
• Parameter types of is.integer and is.safeInteger are narrowed to number, because Integer type extends number type.
  • It has side effect to is.evenInteger, is.oddInteger, and also test cases in is.any are broken.
  • It could be resolved by making Integer type extends unknown.

export type Integer<Type> = Type extends number ?
    `${Type}` extends `${bigint}`
        ? Type
        : never
    : never;

resolve #147

[sindresorhus]

Why are they broken by this change and why would unknown fix it?

[younho9]

Parameter type of is.integer is narrowed to number, so is.integer does not extend Predicate type. is.integer is used in test cases of is.any which require Predicate type function, so broken.

Should I just delete these test cases?

https://github.com/sindresorhus/is/blob/main/test/test.ts#L1528 https://github.com/sindresorhus/is/blob/main/test/test.ts#L1553

[sindresorhus]

is.integer() should still accept unknown, like all the other value checks. If it's unknown, I guess the type guard can simply be number. I don't think we should change the Integer type for this though.

[younho9]

is.integer() should still accept unknown, like all the other value checks. If it's unknown, I guess the type guard can simply be number. I don't think we should change the Integer type for this though.

I agree with your opinion.

[sindresorhus]

Why did you close?

[younho9]

Why did you close?

I think there are some limitation without changing Integer type.

<T>(value: T): value is Integer<T> => Number.isInteger(value);
// => Type 'T' does not satisfy the constraint 'number'

[sindresorhus]

Can't you use an overload?

[younho9]

Unfortunately, inference from a function will only try the last overload signature.

TypeScript Playground

[sindresorhus]

Is this a TypeScript bug/limitation or intentional behavior? If it's a bug/limitation, we could potentially wait for it to be fixed.

[sindresorhus]

Could we do something like this? (Not working)

https://www.typescriptlang.org/play?#code/KYDwDg9gTgLgBDAnmYcCSA7GwDmwoA8AKsqqNhgCYDOcGArgLYBG+AfHALxwAGAJAG8SKAL4845YFVr8BzAJY55WMXAD8cYagBcdYADd8AbgCwAKHOhIsBKXRZc+APJQAqhgDWGCAHcMxUg5uLQkQCho6JlYodXtsPEItDl0GFmNzcwAzegwAYxh5CAw4eWpMePxiUPDaVOi4AB84HK9fDDYACn0AQwAbemBdIgBKXR7+1FK4xygXd1a-Yg4BcwBIKGAYeihigDko-AA6UvKZrr6B4dMzEQyzSmBc3u6NuFyi6ngGXufmXuB9mkoCkDjEmt9etdzPJMh0Tg4Eh0Id0-gDQcNhnAVmY4LjIj8Uf9AdFzCIgA

[younho9]

Is this a TypeScript bug/limitation or intentional behavior? If it's a bug/limitation, we could potentially wait for it to be fixed.

It seems a design limitation. https://github.com/microsoft/TypeScript/issues/45634#issuecomment-912820467

Could we do something like this? (Not working)

typescriptlang.org/play?#code/KYDwDg9gTgLgBDAnmYcCSA7GwDmwoA8AKsqqNhgCYDOcGArgLYBG+AfHALxwAGAJAG8SKAL4845YFVr8BzAJY55WMXAD8cYagBcdYADd8AbgCwAKHOhIsBKXRZc+APJQAqhgDWGCAHcMxUg5uLQkQCho6JlYodXtsPEItDl0GFmNzcwAzegwAYxh5CAw4eWpMePxiUPDaVOi4AB84HK9fDDYACn0AQwAbemBdIgBKXR7+1FK4xygXd1a-Yg4BcwBIKGAYeihigDko-AA6UvKZrr6B4dMzEQyzSmBc3u6NuFyi6ngGXufmXuB9mkoCkDjEmt9etdzPJMh0Tg4Eh0Id0-gDQcNhnAVmY4LjIj8Uf9AdFzCIgA

In this example, if value type is string or something, signature could be function isInteger<string>(value: string): value is number which return type doesn't match with input type.

[sindresorhus]

@younho9 Is there any way we can move this forward or should I close?

[younho9]

I couldn't find a way to solve it. I think you'd better close.