要点

• interface关键字用来定义一个接口
• Go没有implements、extends等关键字
• 实现一个接口的方法就是直接定义接口中的方法
• 要实现多态,就要用指针或&object语法

示例

package main
import "fmt"
import "math"
type Shape interface {
 area() float64 
}
type Circle struct {
 r float64 
}
func (c *Circle) area() float64 {
 return math.Pi * c.r * c.r
}
type Rectangle struct {
 length, width float64 
}
func (r *Rectangle) area() float64 {
 return r.length * r.width;
}
func totalArea(shapes ... Shape) (total float64) {
 total = 0 
 for _, shape := range shapes {
 total += shape.area()
 }
 return 
}
func main() {
 circle := Circle{r:5}
 ractangle := Rectangle{3, 4}
 /*.\helloworld.go:40: cannot use circle (type Circle) as type Shape in argument to totalArea:
 Circle does not implement Shape (area method has pointer receiver)
 fmt.Println(totalArea(circle, ractangle)) // L40 */
 fmt.Println(totalArea(&circle, &ractangle))
}

再论传值与传引用

在上面的代码中,注意到totalArea()声明的类型是Shape,但在后面调用的时候传入的是&cirlce这种。因此,冒出来一个疑问:为什么一个是"对象",一个是地址(指针),却能够运行呢?

曾经考虑过是否Go和Java一样,存在基本类型和对象(用户自定义等)传值、传引用的区别。。。为此,有下面一系列的验证。

基本类型

package main
import "fmt"
func foo(i int) {
 fmt.Println(i)
}
func main() {
 i := 5 
 foo(i)
 /* cannot use &i (type *int) as type int in argument to foo
 foo(&i)*/
}

结构体类型

package main
import "fmt"
type Data struct {
 x int
}
func (data* Data) debug() {
 fmt.Println(data.x)
}
func foo(data Data) {
 data.x++
}
func bar(data *Data) {
 data.x++
}
func main() {
 data := Data{1}
 data.debug()
 // cannot use &data (type *Data) as type Data in argument to foo
 //foo(&data)
 foo(data)
 data.debug()
}

特殊的interface

package main
import "fmt"
type Debugger interface {
 debug()
}
type Data struct {
 x int
}
func (data* Data) debug() {
 fmt.Println(data.x)
}
func foo(debugger Debugger) {
 debugger.debug()
}
func bar(debugger *Debugger) {
 //debugger.debug undefined (type *Debugger is pointer to interface, not interface)
 //debugger.debug()
 (*debugger).debug()
 //syntax error: unexpected >, expecting expression
 //debugger->debug()
}
func main() {
 data := Data{1}
 data.debug()
 /*cannot use data (type Data) as type Debugger in argument to foo:
 Data does not implement Debugger (debug method has pointer receiver)*/
 //foo(data)
 foo(&data)
 /*cannot use &data (type *Data) as type *Debugger in argument to bar:
 *Debugger is pointer to interface, not interface*/
 //bar(&data)
 /*cannot use data (type Data) as type *Debugger in argument to bar:
 *Debugger is pointer to interface, not interface*/
 //bar(data)
}

约定俗成(???)

假定接口为:

type I interface {...}

实现该接口的类为:

type Concreate struct {...}

仅依赖于接口的函数:

func foo(i I) {...}

调用约定:

concreate := Concreate {...}
foo(&concreate)

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