How do I convert a generic struct to the same generic struct of a different type in Golang?

Question

Lets jump straight into a code snippet.

type Animal[T any] struct {
    Name string
    Type string
    Params T
}

type DogParams struct {
    TailLength int
}

type CatParams struct {
    MeowVolume int
}

type Dog = Animal[DogParams]
type Cat = Animal[CatParams]
type Tiger = Animal[CatParams]

var animals = []Animal[any]{
    {
        Name:   "biggie doggie",
        Type:   "dog",
        Params: DogParams{TailLength: 5},
    },
    {
        Name:   "persia",
        Type:   "cat",
        Params: CatParams{MeowVolume: 2},
    },
}

What is the best way to convert an animal from Animal[any] to Animal[CatParams] ?

I have tried

cat, ok := any(animals[1]).(Cat)

and it's not ok.

Thanks in advance!

Basically there is no way (except doing it manually) Even with parametric polymorphism Go is still statically typed and there is no type conversion between any and DogParam. — Volker, Oct 17 '22 at 04:50
You can cast to `Cat` only instances of type `Cat`. It is a named type, and by the rules of Go it is unique. No other types, event with the same fields, could be casted to it. That means, the anonympus type `Animal[any]` can't be casted to `Cat`. — Pak Uula, Oct 17 '22 at 04:53

score 0 · Accepted Answer · answered Oct 17 '22 at 04:58

Following the comments from @Volker and @Pak Uula, you can stick them in an interface{} slice, but this isn't run-time dynamic typing. A Cat is still a Cat:

var animals = []interface{}{
    Dog{
        Name:   "biggie doggie",
        Type:   "dog",
        Params: DogParams{TailLength: 5},
    },
    Cat{
        Name:   "persia",
        Type:   "cat",
        Params: CatParams{MeowVolume: 2},
    },
}

How do I convert a generic struct to the same generic struct of a different type in Golang?

1 Answers1