如何使用Golang函数闭包和匿名函数_封装临时变量和逻辑

base := "/api/v1"
paths := []string{}
for _, suffix := range []string{"users", "posts", "comments"} {
    // 每次迭代创建新闭包，捕获当前 suffix 和 base
    fullPath := func(s string) string {
        return base + "/" + s
    }(suffix)
    paths = append(paths, fullPath)
}
// paths == ["/api/v1/users", "/api/v1/posts", "/api/v1/comments"]

// 创建一个计数器闭包
newCounter := func() func() int {
    count := 0
    return func() int {
        count++
        return count
    }
}
counterA := newCounter()
counterB := newCounter()
fmt.Println(counterA()) // 1
fmt.Println(counterA()) // 2
fmt.Println(counterB()) // 1 —— 独立状态

// 封装带默认重试次数的 HTTP 请求逻辑
makeRequester := func(baseURL string, maxRetries int) func(path string) error {
    client := &http.Client{Timeout: 5 * time.Second}
    return func(path string) error {
        url := baseURL + path
        for i := 0; i <= maxRetries; i++ {
            resp, err := client.Get(url)
            if err == nil && resp.StatusCode == 200 {
                resp.Body.Close()
                return nil
            }
            if i == maxRetries {
                return fmt.Errorf("failed after %d tries: %v", maxRetries, err)
            }
            time.Sleep(time.Second * time.Duration(i+1))
        }
        return nil
    }
}
githubReq := makeRequester("https://www./link/e41bbd4af5da30044b88dc9ab711c5b2", 3)
err := githubReq("/users/octocat")

// ❌ 错误：所有 goroutine 打印最后一个 v
for _, v := range []string{"a", "b", "c"} {
    go func() {
        fmt.Println(v) // 总是 "c"
    }()
}
// ✅ 正确：用局部变量隔离
for _, v := range []string{"a", "b", "c"} {
v := v // 显式复制
go func() {
fmt.Println(v) // 输出 a b c
}()
}