Can you pass a generic type as a parameter for another generic in Java?

Simply provide a generic type like a callback:

type FUNC<ARG,RET, F> = (arg: ARG) => F<RET>;
type PROMISE<T> = Promise<T>;
type IDENT<T> = T;
type A = FUNC<number, void, IDENT>;
type A_PROMISE = FUNC<number, void, PROMISE>;

Could this be done?

Answer №1

Currently, it is not possible to achieve this. There was a discussion regarding this matter back in 2014. For more information, you can refer to this issue.


If you want to restrict the return type, you can try the following:

type FUNC<ARG,RET extends Promise<any>> = (arg: ARG) => RET;

To extract the wrapped type, you can use the following approach:

type PromiseType<T> = T extends Promise<infer T> ? T : never

type A = Promise<string>
type B = PromiseType<A> // string

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