Deduce the type of a generic class

Let's consider the following scenario:

type AnyFunction = (...args: any[]) => any;

abstract class Foo<F extends AnyFunction> {}

class Bar extends Foo<() => string> {}

In addition, there is a function like this:

function foo<F extends AnyFunction>(foo: Foo<F>): void {}

When calling foo(), the desired outcome is to have accurate type inference. For instance, when invoking foo(new Bar()), the expected result would be for the type () => string to be inferred as the generic parameter T</code in <code>foo. However, TypeScript defaults to using AnyFunction, which is the least specific type.

Is there a way to resolve this issue? The goal is to maintain the ability to call foo() accordingly while ensuring that T is correctly inferred as () => string.

Answer №1

F is not being utilized within the class. It is important to make use of type parameters in order to ensure that the structure of the class aligns with the expected types.

By using the type parameter, you will achieve the desired type:

type AnyFunction = (...args: any[]) => any;

abstract class Foo<F extends AnyFunction> {
    f!: F
}

class Bar extends Foo<() => string> {}

function foo<F extends AnyFunction>(arg: Foo<F>): void {}

foo(new Bar) // foo<() => string>(foo: Foo<() => string>)

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