Go interface 例子

定义接口时，列出所有必需的函数。其他不同的数据类型只要实现了此接口中列出的函数，就能成为此接口类型。

以下的 code，虽然 cat 和 dog 属于不同的类型，但是二者都实现了 Animal 接口指定的 Says() 和 HowManyLegs() 函数，所以 cat 和 dog 都是Animal 类型，所以都能作为参数传递给要求 Animal 类型参数的函数 Riddle：

package main

import "fmt"

// interface type
type Animal interface {
    
    
	Says() string
	HowManyLegs() int
}

// Dog is the type for dogs
type Dog struct {
    
    
	Name         string
	Sound        string
	NumberOfLegs int
}

// Says is required by the Animal interface
func (d *Dog) Says() string {
    
    
	return d.Sound
}

// HowManyLegs is required by the Animal interface
func (d *Dog) HowManyLegs() int {
    
    
	return d.NumberOfLegs
}

// Cat is the type for cats
type Cat struct {
    
    
	Name         string
	Sound        string
	NumberOfLegs int
	HasTail      bool
}

// Says is required by the Animal interface
func (c *Cat) Says() string {
    
    
	return c.Sound
}

// HowManyLegs is required by the Animal interface
func (c *Cat) HowManyLegs() int {
    
    
	return c.NumberOfLegs
}

func main() {
    
    
	// create a variable of type Dog
	dog := Dog{
    
    
		Name:         "dog",
		Sound:        "woof",
		NumberOfLegs: 4,
	}

	// Pass dog to riddle. Although dog is of type Dog, it satisifies the
	// interface requirements for Animal because it implements all of Animal's required functions.
	Riddle(&dog)

	// Create  variable of type Cat
	var cat Cat
	cat.Name = "cat"
	cat.NumberOfLegs = 4
	cat.Sound = "meow"
	cat.HasTail = true

	// Pass cat to riddle. Although cat is of type Cat, it satisifies the
	// interface requirements for Animal because it implements all of Animal's required functions.
	Riddle(&cat)
}

// Riddle takes a parameter of type Animal, but will accept both Dog and Cat, since both of those types
// satisfy the interface requirements for Animal, because they both have the correct functions.
func Riddle(a Animal) {
    
    
	riddle := fmt.Sprintf(`This animal says "%s" and has %d legs. What animal is it?`, a.Says(), a.HowManyLegs())
	fmt.Println(riddle)
}