If a pointer type implements a method in an interface, then its value type variable cannot be assigned to the corresponding interface. But it works the other way around!

[王谦铭]

If a pointer type implements a method in an interface, then its value type variable cannot be assigned to the corresponding interface. Conversely, if a value type implements a method in an interface, its pointer type variable can be assigned to the corresponding interface. 

I want know why that can work? Just like the code. 

import "fmt"

type A struct {
}

type Changer1 interface {
change1()
}

type Changer2 interface {
change2()
}

func (a *A) change1() {
}

func (a A) change2() {
}

func main() {
var c1 Changer1
var c2 Changer2
a1 := A{}
a2 := &A{}
c1 = a1 //Wrong, the compilation failed, because the value type of A does not implement the change1() method, so a1, which is the value type of A, is not a Changer1
c1 = a2

c2 = a1
c2 = a2 //It turned out to be ok, the pointer type of A did not implement the change2() method, but a2, which is a pointer type of A, turned out to be a Changer2

//for compilation
fmt.Println(c1)
fmt.Println(c2)
}

[Ian Lance Taylor]

On Sat, Jun 3, 2023 at 10:05 AM 王谦铭 <wangqian...@gmail.com> wrote:
>
> If a pointer type implements a method in an interface, then its value type variable cannot be assigned to the corresponding interface. Conversely, if a value type implements a method in an interface, its pointer type variable can be assigned to the corresponding interface.
> I want know why that can work? Just like the code.

Please paste code as plain text or as a link to the Go playground. Thanks.

In Go every value method--that is, every method with a value
receiver--is also valid for the pointer type. See
https://go.dev/ref/spec#Method_sets .

Ian

[王谦铭]

Thanks for your explanation. 

Ian Lance Taylor <ia...@golang.org> 于2023年6月4日周日 01:09写道：