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Conditional types don't work in Mapped types #21863
Description
cc Anders Hejlsberg (@ahejlsberg)
TypeScript Version: 2.7.0-dev.20180210
Search Terms:
Code
type Omit<T extends object> = { [P in keyof T]: T[P] extends never ? never : P; }[keyof T];
type Omit2<T extends object, U = never> = { [P in keyof T]: T[P] extends U ? never : P; }[keyof T];
type A = Omit<{ a: void; b: never; }>; // 'a' | 'b'
type B = Omit2<{ a: void; b: never; }>; // 'a'Expected behavior:
A is 'a'.
Actual behavior:
A is 'a' | 'b'.
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Activity
falsandtru commentedon Feb 11, 2018
Note: I unawarely updated my example code after a patch is created...