Abstract classes and static methods

The cnb experience

Sunday, March 29. 2009

Posted by Anders Hellstrom in PHP

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Abstract classes and static methods

Working on my TemporalData class, i realized that it should be an abstract class. It's the way I intended to use it all along, but I somehow forgot that PHP now supports abstract classes and didn't define it as such.

The TemporalData class has a couple of static methods used for selecting objects from the database, and I use late static bindings (a php 5.3 feature) to figure out which class the call came through and in turn which table to query. If you were to call one of those methods directly on TemporalData it wouldn't have any way of knowing which table to query, so I used this code to block such calls:

$class = get_called_class();
if ($class == 'TemporalData') {
throw new Exception("TemporalData::open() can not be called directly, only through its subclasses.");
}

I thought I could get rid of this check now that I defined the class to be abstract. Turns out this isn't the case:

abstract class A {
public static function foo() {
echo "I'm in your foo(), eating your bar!\n";
}
}
A::foo();

Output:

I'm in your foo(), eating your bar!

Tested with php 5.2.6 and 5.3.0beta1.

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Who's cnb anyway?

Anders Hellström, also known as cnb, is a systems administrator, web developer and PHP expert working at MrFriday AB, a customized hosting service provider in Stockholm. He lives in Uppsala where he founded the local PHP User Group and has since moved on to become the Chairman of the Board in the local Linux User Group.