在PHP中动态填充静态变量

Question

我有两个静态值:"type"和"typeID".Type是人类可读且常量的,需要根据type的值从数据库中查找typeID.首次加载类定义时,我需要进行一次查找

为了说明,这里有一些代码不起作用,因为你不能在声明空间中调用函数.

MyClass extends BaseClass {
  protected static $type = "communities";
  protected static $typeID = MyClass::lookupTypeID(self::$type);
}

加载类定义时是否有一个神奇的方法被调用一次？如果有明显的东西我会错过它.

Answer 1

无耻地从php手册的静态关键字评论中提取:

Because php does not have a static constructor and you may want to initialize static class vars, there is one easy way, just call your own function directly after the class definition.

for example.

<?php
function Demonstration()
{
    return 'This is the result of demonstration()';
}

class MyStaticClass
{
    //public static $MyStaticVar = Demonstration(); //!!! FAILS: syntax error
    public static $MyStaticVar = null;

    public static function MyStaticInit()
    {
        //this is the static constructor
        //because in a function, everything is allowed, including initializing using other functions

        self::$MyStaticVar = Demonstration();
    }
} MyStaticClass::MyStaticInit(); //Call the static constructor

echo MyStaticClass::$MyStaticVar;
//This is the result of demonstration()
?>