# 将函数作为参数

函数可以作为其它函数的参数进行传递，然后在其它函数内调用执行，一般称之为回调。下面是一个将函数作为参数的简单例子（function\_parameter.go）：

```go
package main

import (
    "fmt"
)

func main() {
    callback(1, Add)
}

func Add(a, b int) {
    fmt.Printf("The sum of %d and %d is: %d\n", a, b, a+b)
}

func callback(y int, f func(int, int)) {
    f(y, 2) // this becomes Add(1, 2)
}
```

输出：

```
The sum of 1 and 2 is: 3
```

将函数作为参数的最好的例子是函数 `strings.IndexFunc()`：

该函数的签名是 `func IndexFunc(s string, f func(c int) bool) int`，它的返回值是在函数 `f(c)` 返回 true、-1 或从未返回时的索引值。

例如 `strings.IndexFunc(line, unicode.IsSpace)` 就会返回 `line` 中第一个空白字符的索引值。当然，您也可以书写自己的函数：

```go
func IsAscii(c int) bool {
    if c > 255 {
        return false
    }
    return true
}
```

在第 14.10.1 节中，我们将会根据一个客户端/服务端程序作为示例对这个用法进行深入讨论。

```go
type binOp func(a, b int) int
func run(op binOp, req *Request) { … }
```

**练习 6.7**

包 `strings` 中的 `Map` 函数和 `strings.IndexFunc()` 一样都是非常好的使用例子。请学习它的源代码并基于该函数书写一个程序，要求将指定文本内的所有非 ASCII 字符替换成 `?` 或空格。您需要怎么做才能删除这些字符呢？

## 链接

* [目录](https://github.com/yangchuansheng/the-way-to-go_ZH_CN/tree/f30ab7d8c58f85840a0afb548024b93642b518d5/eBook/directory.md)
* 上一节：[递归函数](/the-way-to-go-zh-cn/di-er-bu-fen-yu-yan-de-he-xin-jie-gou-yu-ji-shu/06.0/06.6.md)
* 下一节：[闭包](/the-way-to-go-zh-cn/di-er-bu-fen-yu-yan-de-he-xin-jie-gou-yu-ji-shu/06.0/06.8.md)


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