1.11 接口

接口定义与实现

package main

import "fmt"

// 接口定义
type Speaker interface {
    Speak() string
}

// 隐式实现
type Dog struct {
    Name string
}

func (d Dog) Speak() string {
    return "Woof!"
}

type Cat struct {
    Name string
}

func (c Cat) Speak() string {
    return "Meow!"
}

// 接口作为参数
func MakeSpeak(s Speaker) {
    fmt.Println(s.Speak())
}

// 接口作为返回值
func NewPet(name string) Speaker {
    return Dog{Name: name}
}

func main() {
    dog := Dog{Name: "Buddy"}
    cat := Cat{Name: "Kitty"}

    var s Speaker
    s = dog
    fmt.Println(s.Speak())  // Woof!

    s = cat
    fmt.Println(s.Speak())  // Meow!

    // 接口切片
    pets := []Speaker{dog, cat}
    for _, pet := range pets {
        pet.Speak()
    }
}

---

空接口

package main

import "fmt"

func main() {
    // 存储任意类型 (Go 1.18+ 推荐用 any 替代 interface{})
    var x any
    x = 42
    x = "hello"
    x = true

    // 空接口切片
    items := []any{1, "hello", true, 3.14}
    for i, item := range items {
        fmt.Printf("%d: %v (type: %T)\n", i, item, item)
    }

    // 通用函数
    PrintAnything(42)
    PrintAnything("hello")
}

func PrintAnything(x any) {
    fmt.Printf("Value: %v, Type: %T\n", x, x)
}

---

类型断言与类型开关

package main

import "fmt"

func main() {
    // 类型断言
    var x any = "hello"

    s, ok := x.(string)
    fmt.Println(s, ok)  // hello true

    i, ok := x.(int)
    fmt.Println(i, ok)  // 0 false

    // 类型开关
    var values []any = []any{"hello", 42, 3.14, true}

    for _, v := range values {
        switch val := v.(type) {
        case string:
            fmt.Printf("字符串：%s\n", val)
        case int:
            fmt.Printf("整数：%d\n", val)
        case float64:
            fmt.Printf("浮点数：%.2f\n", val)
        case bool:
            fmt.Printf("布尔：%t\n", val)
        default:
            fmt.Printf("未知类型：%T\n", val)
        }
    }
}

---

接口嵌套

package main

import "fmt"

// 接口嵌套
type Reader interface {
    Read(p []byte) (n int, err error)
}

type Writer interface {
    Write(p []byte) (n int, err error)
}

type ReadWriter interface {
    Reader
    Writer
}

type Closer interface {
    Close() error
}

type ReadWriteCloser interface {
    Reader
    Writer
    Closer
}

func main() {
    // 接口设计原则:
    // 1. 接口要小 (单一职责)
    // 2. 接受接口，返回结构体
    // 3. 接口应该在消费者处定义
    // 4. 避免过早抽象
}