该方法是否应该与接口的签名显式地收缩？

I am new with the golang, I am not quite understand why the below demo program could be executed successfully,

type fake interface {
    getAge(valueInt int,  valStr string) (age int, name string, err error)
}

type Foo struct {
    name string
}

func (b *Foo) getAge(valueInt int, valStr string) (age int, retErr error) {
    age = valueInt
    return age, nil
}
func main() {
    inst := &Foo{name:"foo"}
    value, _ := inst.getAge(2, "foo")
    fmt.Println(value)
}

The interface wants to return three value, but the method getAge only return two, but it still works. How to understand this behavior in golang?

Thanks!

Foo doesn't implement fake. This is apparent if you extend your code sample a bit (try it on the Go playground):

package main

import "fmt"

type fake interface {
    getAge(valueInt int, valStr string) (age int, name string, err error)
}

type Foo struct {
    name string
}

func (b *Foo) getAge(valueInt int, valStr string) (age int, retErr error) {
    age = valueInt
    return age, nil
}


func bar(f fake) {
  _, name, _ := f.getAge(10, "")
}

func main() {
    inst := &Foo{name: "foo"}
    value, _ := inst.getAge(2, "foo")
    fmt.Println(value)

    bar(inst)
}

This produces a compile error that's pretty descriptive:

prog.go:28:5: cannot use inst (type *Foo) as type fake in argument to bar:
    *Foo does not implement fake (wrong type for getAge method)
        have getAge(int, string) (int, error)
        want getAge(int, string) (int, string, error)