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=== tests/cases/compiler/promiseIdentity.ts ===
export interface IPromise<T> {
then<U>(callback: (x: T) => IPromise<U>): IPromise<U>;
>then : <U>(callback: (x: T) => IPromise<U>) => IPromise<U>
>callback : (x: T) => IPromise<U>
>x : T
}
interface Promise<T> {
then<U>(callback: (x: T) => Promise<U>): Promise<U>;
>then : <U>(callback: (x: T) => Promise<U>) => Promise<U>
>callback : (x: T) => Promise<U>
>x : T
}
var x: IPromise<string>;
>x : IPromise<string>
var x: Promise<string>;
>x : IPromise<string>
interface IPromise2<T, V> {
then<U, W>(callback: (x: T) => IPromise2<U, W>): IPromise2<W, U>;
>then : <U, W>(callback: (x: T) => IPromise2<U, W>) => IPromise2<W, U>
>callback : (x: T) => IPromise2<U, W>
>x : T
}
interface Promise2<T, V> {
then<U, W>(callback: (x: V) => Promise2<U, T>): Promise2<T, W>; // Uses V instead of T in callback's parameter
>then : <U, W>(callback: (x: V) => Promise2<U, T>) => Promise2<T, W>
>callback : (x: V) => Promise2<U, T>
>x : V
}
// Ok because T in this particular Promise2 is any, as are all the U and W references.
// Also, the V of Promise2 happens to coincide with the T of IPromise2 (they are both string).
var y: IPromise2<string, number>;
>y : IPromise2<string, number>
var y: Promise2<any, string>;
>y : IPromise2<string, number>
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