如何定义接收指针的Go接口方法的实现？

Question

The following program runs fine.

package main

import (
    "fmt"
)

type Person interface {
    Hello()
}

type Joker struct {
    Name string
}

func (j Joker) Hello() {
    fmt.Println(j.Name, "says, \"Hello!\"")
}

func main() {
    var j Joker = Joker{"Peter"}
    invokeHello(j)
}

func invokeHello(p Person) {
    p.Hello()
}

Here is the output.

$ go run foo.go
Peter says, "Hello!"

But when I change the Hello method to receive a pointer, I get errors.

package main

import (
    "fmt"
)

type Person interface {
    Hello()
}

type Joker struct {
    Name string
}

func (j *Joker) Hello() {
    fmt.Println(j.Name, "says, \"Hello!\"")
}

func main() {
    var j *Joker = &Joker{"Peter"}
    invokeHello(j)
}

func invokeHello(p *Person) {
    p.Hello()
}

Here are the errors.

$ go run bar.go
# command-line-arguments
./bar.go:21: cannot use j (type *Joker) as type *Person in argument to invokeHello:
    *Person is pointer to interface, not interface
./bar.go:25: p.Hello undefined (type *Person has no field or method Hello)

How can I fix the second program?

Answer 1

func invokeHello(p *Person) {
    p.Hello()
}

p is type *Person, *Joker implement interface Person, revert invokeHello to:

func invokeHello(p Person) {
    p.Hello()
}

this will fix the second program.

I think you have misleading about golang interface type

An interface type specifies a method set called its interface. A variable of interface type can store a value of any type with a method set that is any superset of the interface. Such a type is said to implement the interface.