This article comes from: CSDN blog
Thanks Author: fengfengdiandia
See original: Go Interface
Go Language is not a "traditional" object-oriented programming language: it is not inside 类and 继承concepts.
But the Go language has a very flexible 接口concept, we can achieve a lot through its 面向对象features.
接口 It defines a 方法的集合, but these methods 不包含实现代码, they are 抽象的, there is also the interface 不能包含变量.
Definition Format
The general format definition of the interface:
type Namer interface {
Method1(param_list) return_type
Method2(param_list) return_type
...
}
The above Namer is an interface type.
However, in Go 接口 may have a value, a 接口类型 variable or a 接口值: var ai Namer , ai it is a multiword data structure, its value is nil.
It's essentially a 指针, though not exactly the same thing. Value is a pointer to the interface 非法的will result in coding errors.
类型(Such as structure) implemented method interface method set achieved Namer interface types can be assigned to a variable ai, then the method table pointer points to the interface methods are implemented.
Implementation type of an interface, in addition to the implementation of the interface method, you can also have their own methods.
package main
import "fmt"
type Shaper interface {
Area() float64
// Perimeter() float64
}
type Rectangle struct {
length float64
width float64
}
// Implementation Shaper interface
func (r *Rectangle) Area() float64 {
return r.length * r.width
}
// Set belongs Rectangle own way
func (r *Rectangle) Set(l float64, w float64) {
r.length = l
r.width = w
}
func main() {
rect := new(Rectangle)
rect.Set(2, 3)
areaIntf := Shaper(rect)
fmt.Printf("The rect has area: %f\n", areaIntf.Area())
}
If you remove Shaper the Perimeter() float64 comments, you will encounter the following compile time error, because Rectangle not implemented Perimeter() method.
cannot convert rect (type *Rectangle) to type Shaper: *Rectangle does not implement Shaper (missing Perimeter method)Polymorphism
1, a plurality of types can implement the same interface.
2, a plurality of types of interfaces may be achieved.
Here we add a type Triangle, it is also implemented as Shaper an interface.
package main
import "fmt"
type Shaper interface {
Area() float64
// Perimeter() float64
}
// ==== Rectangle ====
type Rectangle struct {
length float64
width float64
}
// Implementation Shaper interface
func (r *Rectangle) Area() float64 {
return r.length * r.width
}
// Set belongs Rectangle own way
func (r *Rectangle) Set(l float64, w float64) {
r.length = l
r.width = w
}
// ==== Rectangle End ====
// ==== Triangle ====
type Triangle struct {
bottom float64
hight float64
}
func (t *Triangle) Area() float64 {
return t.bottom * t.hight / 2
}
func (t *Triangle) Set(b float64, h float64) {
t.bottom = b
t.hight = h
}
// ==== Triangle End ====
func main() {
rect := new(Rectangle)
rect.Set(2, 3)
areaIntf := Shaper(rect)
fmt.Printf("The rect has area: %f\n", areaIntf.Area())
triangle := new(Triangle)
triangle.Set(2, 3)
areaIntf = Shaper(triangle)
fmt.Printf("The triangle has area: %f\n", areaIntf.Area())
}
flexibility
Definition of the interface is more flexible.
Suppose in different types of interfaces, and packages, as long as the type implements all the methods in an interface, then it implements this interface.
Now we will Shaper define in shaper 包 the next, Rectangle and Triangle the definition on the test 包 next:
[root@ src]# tree
├── test
│ └── test.go
├── main.go
└── shaper
└── shaper.go
shaper.gopackage shaper
type Shaper interface {
Area() float64
}
test.gopackage test
// ==== Rectangle ====
type Rectangle struct {
length float64
width float64
}
// interface method to achieve Shaper
func (r *Rectangle) Area() float64 {
return r.length * r.width
}
// Set belongs Rectangle own way
func (r *Rectangle) Set(l float64, w float64) {
r.length = l
r.width = w
}
// ==== Rectangle End ====
// ==== Triangle ====
type Triangle struct {
bottom float64
hight float64
}
func (t *Triangle) Area() float64 {
return t.bottom * t.hight / 2
}
func (t *Triangle) Set(b float64, h float64) {
t.bottom = b
t.hight = h
}
// ==== Triangle End ====
// main.go
package main
import (
"fmt"
"shaper"
"test"
)
func main() {
rect := new(test.Rectangle)
rect.Set(2, 3)
areaIntf := shaper.Shaper(rect)
fmt.Printf("The rect has area: %f\n", areaIntf.Area())
triangle := new(test.Triangle)
triangle.Set(2, 3)
areaIntf = shaper.Shaper(triangle)
fmt.Printf("The triangle has area: %f\n", areaIntf.Area())
}
Now run main.go to see the results of it, uh-huh, no problem, ^ _ ^
The rect has area: 6.000000
The triangle has area: 3.000000Nesting Interface
An interface may comprise one or more other interfaces, which corresponds directly to the interfaces of these methods embedded in the outer layer include the same interface.
For example, the interface File includes ReadWrite and Lock all methods, it also has an additional Close() method.
type ReadWrite interface {
Read(b Buffer) bool
Write(b Buffer) bool
}
type Lock interface {
Lock()
Unlock()
}
type File interface {
ReadWrite
Lock
Close()
}
Type assertion
If I wrote a structure type MyFile to achieve the above File interface, how do I know MyFile whether to implement the File interface to it?
Usually we use 类型断言 to test at some point varI whether to include types of T values:
if v, ok : = varI.(T) ; ok { // checked type assertion
Process(v)
return
}
// varI is not of type T
If you v are varI converting to the type of T value ok will be true; otherwise it v is the type of T zero value, ok is false.
// main.gopackage main
import "fmt"
type MyFile struct{}
func (m *MyFile) Read() bool {
fmt.Printf("Read()\n")
return true
}
// ...
// Let's say I have achieved here Write (), Lock (), Unlock () and Close () method
func main() {
my := new(MyFile)
fIntf := File(my)
// look here, look here
if v, ok := fIntf.(*MyFile); ok {
v.Read()
}
}
The output is: Read ()
If more than one type implements the same interface, such as front areaIntf, how to test it?
Then use type-switch to judge.
type-switch type judgment
switch t := areaIntf.(type) {
case *Rectangle:
// do something
case *Triangle:
// do something
default:
// do something
}