I don't understand typeparams

Getting Help
1

Hi, I don’t know the relationship of typeparams to type switches, and typeparams as thing for fast code.

I’m looking for the Go equivalent to C++ function overloading and C++ resolving the types at compile-time.

May I post a C++ example that I want to implement in Go?

foo(int a) { /* do int things */ }
foo(float a) { /* do float things */ }

So, if I want this example from above in Go, with type checking at runtime (slow, unwanted), I can write:

func foo(a interface{}) {
	switch v := i.(type) {
	case int:
	case float32:
	default:
	}
}

That is old Go, and now in new Go I can also write (fast) code like this?

func foo[T any](a T) {
	switch v := a.(type) {
	case int:
	case float32:
	default:
	}
}

This looks like there would be type checking at runtime (unwanted), and maybe the type switch will not compile. Should have checked it myself but I need to learn generic Go in general, so I’m asking.

I have not read the right design document in the Go documentation. I’m not sure what the Go team tried to solve and what not. I tried to use any function overloading that might have been in Go and the compiler told me I’m redeclaring functions and this is not how it goes.

2

Go does not have function overloading, so the answer depends on what foo(int) and foo(float) do. If they have different implementations, e.g.:

int foo(int a) { return a + a; }
float foo(float a) { return a * a; }

Then they should be separate functions in Go:

func fooInt(a int) { return a + a }
func fooFloat(a float32) { return a * a }

If they both do the same thing, just with different types, then I think the Go 1.18+ way to do this would be to use generics with a type constraint:

type intOrFloat32 interface {
    int | float32
}

func foo[T intOrFloat32](a T) { return a * a }
1 Like
3

Thank you so much.

Something of the generics or constraints that Go 1.18 introduces is a bit hard to grasp, and it leads me into various directions, and to be honest it’s likely that I will prefer that C-style without the new generics. I simply don’t know the design criteria they followed, and the code looks like I will not understand it without investing months and years.

4

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