如何在PHP中实现只读成员变量? [英] How to implement a read-only member variable in PHP?

问题描述

尝试更改它时，引发异常.

When trying to change it,throw an exception.

推荐答案

对于类属性，我想一个解决方案是:

I suppose a solution, for class properties, would be to :

• 不使用您感兴趣的名称定义属性
• 使用神奇的__get方法，使用假"名称访问该属性
• 定义__set方法，以便在尝试设置该属性时抛出异常.
• 有关魔术方法的更多信息，请参见重载.
li>

• not define a property with the name that interests you
• use the magic __get method to access that property, using the "fake" name
• define the __set method so it throws an exception when trying to set that property.
• See Overloading, for more informations on magic methods.

对于变量，我认为不可能有一个只读变量，当您尝试向其写入数据时，PHP会对该变量抛出异常.

For variables, I don't think it's possible to have a read-only variable for which PHP will throw an exception when you're trying to write to it.

例如，考虑这个小类:

For instance, consider this little class :

class MyClass {
    protected $_data = array(
        'myVar' => 'test'
    );

    public function __get($name) {
        if (isset($this->_data[$name])) {
            return $this->_data[$name];
        } else {
            // non-existant property
            // => up to you to decide what to do
        }
    }

    public function __set($name, $value) {
        if ($name === 'myVar') {
            throw new Exception("not allowed : $name");
        } else {
            // => up to you to decide what to do
        }
    }
}

实例化该类并尝试读取该属性:

Instanciating the class and trying to read the property :

$a = new MyClass();
echo $a->myVar . '<br />';

将为您带来预期的输出:

Will get you the expected output :

test

在尝试写入属性时:

$a->myVar = 10;

会给你一个例外:

Exception: not allowed : myVar in /.../temp.php on line 19

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