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Conditional types works incorrectly when generics with constraints #24190
Description
TypeScript Version: 2.8.1, 2.9.0-dev.20180516
Search Terms: Conditional Types, generics
Code
strictFunctionTypes: true
type NonFunctionPropertyNames<T> = { [K in keyof T]: T[K] extends Function ? never : K }[keyof T];
type NonFunctionProperties<T> = Pick<T, NonFunctionPropertyNames<T>>;
interface Interface1
{
}
class Class1<T extends Interface1>
{
private prop1: NonFunctionProperties<T>|null = null;
public method1(): Class1<Interface1>
{
return this; // <- error TS2322
}
}Expected behavior:
No error
Actual behavior:
Error:(15, 9) TS2322: Type 'this' is not assignable to type 'Class1<Interface1>'.
Type 'Class1<T>' is not assignable to type 'Class1<Interface1>'.
Type 'Interface1' is not assignable to type 'T'.
Playground Link:
Need to enable strictFunctionTypes in Options
Playground
Related Issues:
Activity
mhegazy commentedon Jul 18, 2018
This is the result of
--strictFunctionTypesclassClass1is contravariant with respect toT, sinceTis used in contravarient location (i.e.keyof T). The result is thatInterface1needs to be assingbale tothis, which is not true.typescript-bot commentedon Jul 30, 2018
Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.