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strictFunctionTypes option should strictly check callback parameters of override methods #19007
Description
As Aluan Haddad (@aluanhaddad) mentioned at #19004 (comment).
cc Anders Hejlsberg (@ahejlsberg)
TypeScript Version: master
Code
class C {
a(f: (a: C) => C): void {
}
}
class D extends C {
p: boolean = true;
a(f: (a: D) => D): void { // should throw an error here.
console.log(this.p);
this.p = f(new D()).p; // type is boolean, but value is undefined.
console.log(this.p);
}
}
const c: C = new D();
c.a(() => new C());Expected behavior:
error
Actual behavior:
$ node built/local/tsc.js index.ts --strictFunctionTypes && node index.js
true
undefined
Activity
ahejlsberg commentedon Oct 7, 2017
This is working as intended. As explained here, in
--strictFunctionTypesmode we still check parameters of methods and constructors bivariantly. So, there is no error here:But an error is reported here:
As I explain here, we can't tighten this any further without causing
Array<T>and other core types to become invariant.falsandtru commentedon Oct 7, 2017
I see, thanks for your explanation.