Re: [go-nuts] 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]

Thanks for your explanation.

Ian Lance Taylor  于2023年6月4日周日 01:09写道：

> On Sat, Jun 3, 2023 at 10:05 AM 王谦铭  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
>

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[go-nuts] 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)
}

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