PHP 属性的运行时实例化与反射机制

<?php
#[Attribute]
class exampleAttribute
{
    public function __construct()
    {
        echo "exampleAttribute called\n";
    }
}

#[exampleAttribute()]
function exampleFunction()
{
    // ... 函数逻辑
}

// 在这里，exampleAttribute 的构造函数并不会被自动调用
echo "Function defined, but attribute constructor not yet called.\n";
?>

<?php

// 1. 定义属性类
#[Attribute] // 声明这是一个属性类，可以在其他代码元素上使用
class exampleAttribute
{
    private string $message;

    public function __construct(string $message = "Default message")
    {
        $this->message = $message;
        echo "exampleAttribute constructor called with message: " . $this->message . "\n";
    }

    public function getMessage(): string
    {
        return $this->message;
    }
}

// 2. 将属性应用于函数
#[exampleAttribute("Hello from attribute!")]
function exampleFunction()
{
    echo "Executing exampleFunction...\n";
    // ... 函数的实际逻辑
}

// 3. 使用反射来检测和实例化属性

// 获取 exampleFunction 的反射对象
$reflectionFunction = new ReflectionFunction('exampleFunction');

// 获取附加到 exampleFunction 上的所有属性
$attributes = $reflectionFunction->getAttributes();

echo "--- Processing Attributes ---\n";

// 遍历并实例化属性
foreach ($attributes as $reflectionAttribute) {
    // 检查是否是我们感兴趣的 exampleAttribute
    if ($reflectionAttribute->getName() === exampleAttribute::class) {
        // 实例化属性类，这将触发其构造函数
        $attributeInstance = $reflectionAttribute->newInstance();

        // 现在你可以与这个实例交互了
        echo "Attribute instance message: " . $attributeInstance->getMessage() . "\n";
    }
}

echo "--- Attribute Processing Complete ---\n";

// 4. 调用函数（可选，与属性实例化无关）
exampleFunction();

?>

--- Processing Attributes ---
exampleAttribute constructor called with message: Hello from attribute!
Attribute instance message: Hello from attribute!
--- Attribute Processing Complete ---
Executing exampleFunction...