Generic function, can't be defined in form of anonymous?

Question

e.g:

func f[T any](t T) T {
    var result T
    return result
}

// this got error !
var fAnonymous = func[T any](t T) T {
    var result T
    return result
}

fAnonymous got error, it says:

Function literal cannot have type parameters

So, why golang don't permit a anonymous function to be generic?

Answer 1

A function literal cannot be generic because the function literal produces a function value, and the function value cannot be generic. Similarly, if you have a generic function, you cannot use it as a function value. For example

func RegularFunction() {}
func GenericFunction[T any]() {}

func main() {
    // fine, since regular function can act as a value
    var f1 func() = RegularFunction
    // not valid, since a generic function is not a function value
    // Error: "cannot use generic function GenericFunction without instantiation"
    var f2 func() = GenericFunction
    // fine, since the generic function has been instantiated
    var f3 func() = GenericFunction[int]
}

To put it another way:

//             vvvvvvvvvvvvv this is the type of normalFunc
var normalFunc func(int) int = func(i int) int {
    return i + 1
}

//              vvvvvv what type would go here?
var genericFunc        = func[T any](t T) T {
    var result T
    return result
}

The variable fAnonymous cannot be given any type here. Generic functions are not a type in the Go type system; they are just a syntactic tool for instantiating functions with type substitution.