golang接口基础用法

定义

接口是一组包含方法名，参数，返回值的未具体实现方法的集合

基础用法如下：

package main

import (
    "fmt"
)

type Schooler interface {
    Name() string
    Age() int
    Grade() int
}

type Student struct {
    name  string
    age   int
    grade int
}

func (s Student) Name() string {
    return s.name
}

func (s Student) Age() int {
    return s.age
}

func (s Student) Grade() int {
    return s.grade
}

func main() {
    var school Schooler
    student := Student{name: "Jack", age: 10, grade: 4}
    // 因为student实现了Schooler接口所以直接赋值没问题
    school = student
    fmt.Printf("name:%v,age:%v,grade:%v\n", school.Name(), school.Age(), school.Grade()) // name:Jack,age:10,grade:4
}

空接口

空接口不包含任何方法，因此， 任意类型均实现了空接口 。

任意类型变量都可以赋值给空接口类型的变量，如下所示：

package main

import (
    "fmt"
)

type Typer interface{}

func main() {
    var tt Typer
    var a int
    var b float32

    tt = a
    fmt.Printf("%T\n", tt) // int
    tt = b
    fmt.Printf("%T\n", tt) // float32
}

测试接口实现

测试变量是否实现了某个接口需要使用 x.(T) 的特定语法，如下所示：

package main

import (
    "fmt"
)

type Schooler interface {
    Name() string
    Age() int
}

type Student struct {
    name string
    age  int
}

type Teacher struct {
    name string
    age  int
}

func (s Student) Name() string {
    return s.name
}

func (s Student) Age() int {
    return s.age
}

func (s Teacher) Name() string {
    return s.name
}

func CheckSchoolerImpliments(v interface{}) bool {
    if tmp, ok := v.(Schooler); ok {
        fmt.Printf("%T, %v", tmp, tmp)
        return true
    }
    return false
}

func main() {
    student := Student{name: "Jack", age: 10}
    teacher := Teacher{name: "Lucy", age: 26}
    fmt.Println(CheckSchoolerImpliments(student)) // main.Student, {Jack 10}true
    fmt.Println(CheckSchoolerImpliments(teacher)) // false
}

类型断言

空接口可以存储任意类型，区分不同的类型常用两种方法， Comma-ok断言 和 switch判断

package main

import (
    "fmt"
)

type Student struct {
    name string
}

func main() {
    var params = make([]interface{}, 3)
    fmt.Println(params) // [<nil> <nil> <nil>]
    params[0] = 18
    params[1] = "hello"
    params[2] = Student{name: "Jack"}
    fmt.Println(params) // [18 hello {Jack}]

    for _, item := range params {
        if _, ok := item.(int); ok {
            fmt.Printf("%v's type is int\n", item) // 18's type is int
        } else if _, ok := item.(string); ok {
            fmt.Printf("%v's type is string\n", item) // hello's type is string
        } else if _, ok := item.(Student); ok {
            fmt.Printf("%v's type is struct\n", item) // {Jack}'s type is struct
        }
    }

    for _, item := range params {
        switch value := item.(type) {
        case int:
            fmt.Printf("%v's type is int\n", value) // 18's type is int
        case string:
            fmt.Printf("%v's type is string\n", item) // hello's type is string
        case Student:
            fmt.Printf("%v's type is struct\n", item) // {Jack}'s type is struct
        default:
            fmt.Printf("unknown type\n")
        }
    }
}

接口零值

未赋值的接口类型为 nil

package main

import (
    "fmt"
)

type Student interface {
    name() string
}

func main() {
    var s Student
    if s == nil {
        fmt.Println("s is nil") // s is nil
    }
}

指针实现接口与值实现接口

package main

import (
    "fmt"
)

type Schooler interface {
    Name() string
    Age() int
}

type Student struct {
    name string
    age  int
}

type Teacher struct {
    name string
    age  int
}

func (s Student) Name() string {
    return s.name
}

func (s Student) Age() int {
    return s.age
}

func (s *Teacher) Name() string {
    return s.name
}

func (s *Teacher) Age() int {
    return s.age
}

func main() {
    student := Student{name: "Jack", age: 10}
    teacher := Teacher{name: "Lucy", age: 26}

    var s Schooler
    s = student
    fmt.Printf("name:%v.age:%v\n", s.Name(), s.Age()) // name:Jack.age:10
    // s = teacher // Teacher does not implement Schooler, *Teacher does
    s = &teacher
    fmt.Printf("name:%v.age:%v\n", s.Name(), s.Age()) //name:Lucy.age:26
}

接口嵌套

package main

import (
    "fmt"
)

type Peopler interface {
    Name() string
    Age() int
}

type Schooler interface {
    Peopler
    Role() string
}

type Student struct {
    name string
    age  int
}

type Teacher struct {
    name string
    age  int
}

func (s Student) Name() string {
    return s.name
}

func (s Student) Age() int {
    return s.age
}

func (s Student) Role() string {
    return "Student"
}

func main() {
    student := Student{name: "Jack", age: 10}

    var p Peopler
    var s Schooler
    p = student
    fmt.Printf("name:%v, age:%v\n", p.Name(), p.Age()) // name:Jack.age:10
    s = student
    fmt.Printf("name:%v, age:%v, role:%v\n", s.Name(), s.Age(), s.Role()) // name:Jack, age:10, role:Student
}

参考： https://studygolang.com/articles/20117