Question

I have two static values: “type” and “typeID”. Type is human readable and constant, and typeID needs to be looked up from the database, based on the value of type. I need the lookup to happen once, when the class definition is first loaded

To illustrate, here is some code that doesn’t work because you can’t call functions in the declaration space.

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

Is there a magic method that is called exactly once when the class definition is loaded? If there is something obvious I’m missing it.

Answer 1

shamelessly pulled from the php manual’s static keyword comments:

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()
?>