具有相同名称和类型但类型不同的Golang方法

Question

The following code works fine. Two methods operating on two different structs and printing a field of the struct:

type A struct {
  Name string
}

type B struct {
  Name string
}

func (a *A) Print() {
  fmt.Println(a.Name)
}

func (b *B) Print() {
  fmt.Println(b.Name)
}

func main() {

  a := &A{"A"}
  b := &B{"B"}

  a.Print()
  b.Print()
}

Shows the desired output in the console:

A
B

Now, if I change the method signature in the following way I get an compile error. I just move the receiver of the method to the arguments of the method:

func Print(a *A) {
  fmt.Println(a.Name)
}

func Print(b *B) {
  fmt.Println(b.Name)
}

func main() {

  a := &A{"A"}
  b := &B{"B"}

  Print(a)
  Print(b)
}

I can't even compile the program:

./test.go:22: Print redeclared in this block
    previous declaration at ./test.go:18
./test.go:40: cannot use a (type *A) as type *B in function argument

Question: Why is it, that I can interchange struct types in the receiver, but not in the arguments, when the methods have the same name and arity?

Answer 1

Because Go does not support overloading of user-defined functions on their argument types.

You can make functions with different names instead, or use methods if you want to "overload" on only one parameter (the receiver).