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[typescript - 2.4] Strict contravariance for callback parameters #50

Open sculove opened 7 years ago

sculove commented 7 years ago 
interface Mappable<T> {
    map<U>(f: (x: T) => U): Mappable<U>;
}

declare let a: Mappable<number>;
declare let b: Mappable<string | number>;

a = b; // should fail, now does.
b = a; // should succeed, continues to do so.