这两个Go代码段是否等效？

Question

Having this struct

type Square struct {
    Side int
}

Are these to functions equivalent?

func (s *Square) SetSide(side int) {
    s.Side = side
}

vs

func SetSquareSide(s *Square, side int) {
    s.Side = side
}

I know they do the same, but are they really equivalent? I mean, is there any internal difference or something?

Try online: https://play.golang.org/p/gpt2KmsVrz

Answer 1

These "function" the same way, and in reality they are called in nearly the same way. The method is called as a method expression, with the receiver as the first argument:

var s Square

// The method call
s.SetSide(5)
// is equivalent to the method expression
(*Square).SetSide(&s, 5)

The SetSide method can also be used as a method value to satisfy the function signature func(int), where as the SetSquareSide cannot.

var f func(int)

f = a.SetSide
f(9)

This is on top of the obvious fact that the method set of Square satisfies the interface

interface {
    SetSide(int)
}