Skip to content

Inconsistent boolean literal types in objectsΒ #59754

Open
@Andarist

Description

@Andarist

πŸ”Ž Search Terms

boolean invariant type parameter literal widen union

πŸ•— Version & Regression Information

  • This is the behavior in every version I tried

⏯ Playground Link

https://www.typescriptlang.org/play/?ts=5.7.0-dev.20240824&ssl=14&ssc=130&pln=1&pc=1#code/PTAECEHsA8B4BUB8oAuBPADgU1ASwM54B2AbgIYBOuZRKxo8AsAFAvrYQwLIC8oA3i1CgA5lhQAuUAAoAlKB7J4AbiGh84qdPIAbAK5Yp8eYtAlIuACarmAXxstLWAMY7KOAGZ6izlLkhEoABGXEjaZPqGDLJSUHBIDszOAfh0QUQAjArBMNL8oBgUkBhSAAygtrLKoCCccPmFxVJEegC2QVgUFYgsyUSpwUQATLFcDUUloC3tnd3ZIdB5BRNlFVU1YADyANYsvSlpQVl8C0uNkx4RGmvVtXGw4005kDpYNN37-YcjdQ-LTyEXm9ArZeDlFo8LlccJVbmAAKIUIoUAA04L+5yklx011BU0gdDI+HwuBERDIQVeqEgv0hUkBr3eoJYQA

πŸ’» Code

// Box<T> type is invariant in T

type Box<T> = {
  get: () => T;
  set: (value: T) => void;
};

declare function box<T>(value: T): Box<T>;

const bn1 = box({ prop: 0 }); // Box<{ prop: number }>
const bn2: Box<{ prop: number }> = box({ prop: 0 }); // Ok

const bb1 = box({ prop: false }); // Box<{ prop: boolean }>
const bb2: Box<{ prop: boolean }> = box({ prop: false }); // Error, box<{ prop: false }> not assignable to Box<{ prop: boolean }>

πŸ™ Actual behavior

Error on bb2 is surprising and inconsistent with lack of error on bn2.

πŸ™‚ Expected behavior

Expected the box(false) expression to have type Box<boolean> for both bb1 and bb2.

Additional information about the issue

This issue is a small variation of #48363 that was fixed by @ahejlsberg in #48380

Metadata

Metadata

Assignees

No one assigned

    Labels

    BugA bug in TypeScriptHelp WantedYou can do this

    Type

    No type

    Projects

    No projects

    Relationships

    None yet

    Development

    No branches or pull requests

    Issue actions