Allow users to customize the variance of built-in Array #52621
Description
Bug Report
🔎 Search Terms
Array covariance hardcoded?, Array invariance, --noLib
🕗 Version & Regression Information
Tested with 4.9.5
⏯ Playground Link
💻 Code
// @noLib: true
interface Array<T>
{ [i: number]: T | undefined
, push: (t: T) => number
}
interface _Array<T>
{ [i: number]: T | undefined
, push: (t: T) => number
}
declare let as: Array<"a">
declare let abs: Array<"a" | "b">
abs = as
declare let _as: _Array<"a">
declare let _abs: _Array<"a" | "b">
_abs = _as🙁 Actual behavior
The assignment abs = as compiles.
🙂 Expected behavior
The assignment abs = as should not compile, just like the assignment _abs = _as does not compile.