我可以在一个类中设置一个常量，然后在PHP外部访问它吗？

问题描述：

我试图在类的内部初始化一些值，并将其保存为常量，然后在代码的不同部分访问它们。

I am trying to initialize some values inside a class and save them in constant and access them outside, in different part of my code.

<?php

class Config {

  public static function initialize() {
    define('TEST',"This is a Constant");
  }

}

$config = Config::initialize();
// do something with the constants

我可以在外部访问它吗？

Can I access it outside?

答

Class常量使用 const 关键字。您无需使用define函数对其进行定义。就像这样：

A Class constant uses the const keyword. You don't define them using the define function. Just like this:

class Config {
        const TEST = "This is a constant";
}

// then use it:
var_dump(Config::TEST);

在PHP中，您无法动态设置常量的值，但是可以通过以下方式获得类似的行为公共静态变量。

In PHP, you cannot dynamically set the value of a constant, but you can get a similar behaviour with a public static variable. ie.

class Config2 {
    public static $test = null;
    public static function initialize()
    {
        self::$test = "This is not a constant";
    }
}

// Then use like
Config2::initialize();
var_dump(Config2::$test);

缺点是，没有什么可以阻止其他代码从类外部设置值。如果需要对此进行保护，则应使用吸气剂功能方法。

The downside is, there is nothing stopping other code from setting the value from outside the class. If you need protection against this, you should use a getter function approach. eg.

class Config3 {
    private static $_test = null;
    public static function initialize()
    {
        self::$_test = "This is not a constant, but can't be changed outside this class";
    }

    public static function getTest()
    {
        return self::$_test;
    }
}

// Then use like
Config3::initialize();
var_dump(Config3::getTest());

我可以在一个类中设置一个常量，然后在PHP外部访问它吗？

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