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PHP's __autoload() ( documentation ) is pretty interesting to me. Here's how it works: You try to use a class, like new Toast_Mitten() (footnote 1 ) The class hasn't been loaded into memory. PHP pulls back its fist to sock you with an error. It pauses. "Wait," it says. "There's an __autoload() function defined." It runs it. In that function, you have somehow mapped the string Toast_Mitten to classes/toast_mitten.php and told it to require that file. It does. Now the class is in memory and your program keeps running. Memory benefit: you only load the classes you need. Terseness benefit: you can stop including so many files everywhere and just include your autoloader. Things get particularly interesting if 1) Your __autoload() has an automatic way of determining the file path and name from the class name. For instance, maybe all your classes are in classes/ and Toast_Mitten will be in classes/toast_mitten.php . Or maybe you name classes like Animal_Mammal_Weasel , which will be in classes/animal/mammal/animal_mammal_weasel.php . 2) You use a factory method to get instances of your class. $Mitten = Mitten::factory('toast'); The Mitten::factory method can say to itself, "let's see, do I have a subclass called Toast_Mitten() ? If so, I'll return that; if not, I'll just return a generic instance of myself - a standard mitten. Oh, look! __autoload() tells me there is a special class for toast. OK, here's an instance!" Therefore, you can start out using a generic mitten throughout your code, and when the

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