How Can Generics in Go Handle Functions with Pointer-Based Interface Parameters?

Generic Interface of Pointers

In Go, defining an interface for a pointer implementation can be done through generics. Consider the following scenario:

Problem:

• You have an interface A with a method SomeMethod().
• You have a struct pointer *Aimpl that implements the A interface.
• You want to create a generic function Handler that accepts a function with an A parameter, and assigns a pointer to Aimpl to its parameter.

Solution Using Generic Interface with Type Parameter:

To achieve this, you can declare the A interface with a type parameter, ensuring that the implementing type is a pointer to its type parameter:

type A[P any] interface {
    SomeMethod()
    *P
}

Then, modify the signature of Handler as follows:

func Handler[P any, T A[P]](callback func(result T)) {
    result := new(P)
    callback(result)
}

Solution Using Wrapper Interface:

If you cannot modify the definition of A, you can wrap it into your own interface MyA:

type MyA[P any] interface {
    A
    *P
}

Then, update the signature of Handler to use the MyA interface:

func Handler[P any, T MyA[P]](callback func(result T)) {
    result := new(P)
    callback(result)
}

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