// Go 不需要 class、extends、implements
// 用结构体 + 方法 + 接口 就能实现面向对象的核心能力
type Writer interface {
    Write(p []byte) (n int, err error)
}

type FileWriter struct {
    path string
}

func (f FileWriter) Write(p []byte) (n int, err error) {
    // 实现写入逻辑
    return len(p), nil
}

package main

import "fmt"

func main() {
    // 编译错误：x declared but not used
    // x := 42
    
    // 必须显式使用
    x := 42
    fmt.Println(x)
}

type Animal struct {
    Name string
}

func (a Animal) Speak() string {
    return "..."
}

type Dog struct {
    Animal // 嵌入，而非继承
    Breed  string
}

func main() {
    d := Dog{
        Animal: Animal{Name: "Buddy"},
        Breed:  "Golden Retriever",
    }
    // Dog 自动获得 Animal 的方法
    fmt.Println(d.Name)   // Buddy
    fmt.Println(d.Speak()) // ...
}

package main

import (
    "fmt"
    "time"
)

func worker(id int, jobs <-chan int, results chan<- int) {
    for job := range jobs {
        fmt.Printf("Worker %d processing job %d\n", id, job)
        time.Sleep(time.Millisecond * 100)
        results <- job * 2
    }
}

func main() {
    jobs := make(chan int, 100)
    results := make(chan int, 100)

    // 启动 3 个 worker goroutine
    for w := 1; w <= 3; w++ {
        go worker(w, jobs, results)
    }

    // 发送 5 个任务
    for j := 1; j <= 5; j++ {
        jobs <- j
    }
    close(jobs)

    // 收集结果
    for r := 1; r <= 5; r++ {
        fmt.Println("Result:", <-results)
    }
}

package main

import (
    "fmt"
    "runtime"
    "time"
)

func main() {
    fmt.Println("🎉 欢迎来到 Go 语言的世界！")
    fmt.Println()
    fmt.Printf("Go 版本: %s\n", runtime.Version())
    fmt.Printf("操作系统: %s/%s\n", runtime.GOOS, runtime.GOARCH)
    fmt.Printf("CPU 核心: %d\n", runtime.NumCPU())
    fmt.Println()
    
    // 感受 goroutine 的轻量
    start := time.Now()
    done := make(chan bool)
    
    for i := 0; i < 10000; i++ {
        go func(id int) {
            // 每个 goroutine 仅占用约 2KB 初始栈
            done <- true
        }(i)
    }
    
    for i := 0; i < 10000; i++ {
        <-done
    }
    
    fmt.Printf("创建 10000 个 goroutine 耗时: %v\n", time.Since(start))
}