Repository navigation
Conditional types can't resolve keyof this #21862
Description
cc Anders Hejlsberg (@ahejlsberg)
TypeScript Version: 2.7.0-dev.20180210
Search Terms:
Code
type OldDiff<T extends string, U extends string> = (
& { [P in T]: P; }
& { [P in U]: never; }
& { [x: string]: never; }
)[T];
type NewDiff<T, U> = T extends U ? never : T;
interface A {
a: 'a';
}
interface B1 extends A {
b: 'b';
c: OldDiff<keyof this, keyof A>;
}
interface B2 extends A {
b: 'b';
c: NewDiff<keyof this, keyof A>;
}
type c1 = B1['c']; // 'c' | 'b'
type c2 = B2['c']; // 'c' | 'a' | 'b'Expected behavior:
c2 is 'c' | 'b'.
Actual behavior:
c2 is 'c' | 'a' | 'b'.
Playground Link:
Related Issues:
Activity
falsandtru commentedon Feb 12, 2018
Anders Hejlsberg (@ahejlsberg) Is this not a bug?
ahejlsberg commentedon Feb 12, 2018
falsandtru (@falsandtru) Don't know yet, haven't had time to look.
falsandtru commentedon Feb 12, 2018
I see.