# 第三章、使用 PHP 函数

在本章中，我们将讨论以下主题：

* 函数开发
* 数据类型提示
* 使用返回值数据类型
* 使用迭代器
* 使用生成器编写自己的迭代器

## 引言

在本章中，我们将考虑利用 PHP 的**函数式编程能力**的示例。函数式编程，或者说**程序化编程**，是PHP代码在PHP第4版引入**面向对象编程**（**OOP**）之前的传统编写方式。函数式编程是一种编程范式—一种构建计算机程序结构和元素的风格—它将计算视为数学函数的评估，并避免改变状态和可变数据。然后这个文件可以包含在任何未来的脚本中，允许随意调用定义的函数。


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