Ensure a type implements an interface at compile time in Go

Question

How can I ensure that a type implements an interface at compile time? The typical way to do this is by failure to assign to support interfaces from that type, however I have

Answer 1

package main

import (
    "fmt"
)

type Sayer interface {
    Say()
}

type Person struct {
    Name string
}

func(this *Person) Say() {
    fmt.Println("I am", this.Name)
}

func main() {
    person := &Person{"polaris"}

    Test(person)
}

func Test(i interface{}) {
    //!!here ,judge i implement Sayer
    if sayer, ok := i.(Sayer); ok {
        sayer.Say()
    }
}

The code example is here:http://play.golang.org/p/22bgbYVV6q