Useless compile error on triple-equal 1|2 against 0

TypeScript Version: 2.7.1

Search Terms: infer, compare, equals

Code

type T = [number] | [number, number];  // now t.length has type 1|2
let t: T;
if (t!.length === 0) { // compile error: Operator '===' cannot be applied to types '1' and '0'
}
if (t!.length > 100) { // no compile error
}
if (t!.length === 1 - 1) { // no compile error
}

Expected behavior:
No compile errors on any of these. It's plain inconsistent and not useful.

Actual behavior:
Compile error on t === 0 but not on other comparisons

Playground Link:
See above

Related Issues:

For what it's worth, I would love to see arithmetic constraints on things like lengths. But such an error only really becomes useful when users can write such constraints (I envision writing a function like f(valueThatIsNotEmpty: string & { length: number > 0; }) or something).

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.

Navigation Menu

Repository navigation

Useless compile error on triple-equal 1|2 against 0 #21724

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Useless compile error on triple-equal 1|2 against 0 #21724

Description

Activity

krryan commented on Feb 7, 2018

typescript-bot commented on Feb 22, 2018

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions