A Tour of Go Interfaces

An interface type is defined by a set of methods.

A value of interface type can hold any value that implements those methods.

Note: The code on the left fails to compile.

Vertex doesn't satisfy Abser because the Abs method is defined only on*Vertex, not Vertex.

package main

import (
    "fmt"
    "math"
)
 type Abser interface {
     Abs() float64
 }

 func main() {
     var a Abser
     f := MyFloat(-math.Sqrt2)
     v := Vertex{3, 4}

     a = f // a MyFloat implements Abser
     a = &v  // a *Vertex implements Abser

     // In the following line, v is a Vertex(not *Vertex)
     // and does Not Implement Abser.
     //a = v 
     fmt.Println(a.Abs())
 }

 type MyFloat float64

 func (f MyFloat) Abs() float64 {
     if f < 0 {
         return float64(-f)
     }
     return float64(f)
 }

 type Vertex struct {
     X,Y float64
 }

 func (v *Vertex) Abs() float64 {
     return math.Sqrt(v.X*v.X + v.Y*v.Y)
 }

接口现在的看法越来越是只要这个类 对象 结构或者任何东西它实现了某一些方法组合那么他就实现了这个接口