note 31160 rejected from language.oop by alindeman

A question about the run-time efficiency OOP techniques in PHP: I learned PHP and did a lot of work in it before my current studies in C# and PowerBuilder. In my old PHP code, I reuse code through the use of standard includes, and understand that includes within a conditional clause will only be read in if the clause is executed. Using classes, any object I may wish to instantiate within a clause must have the class definition at the top of the script, possibly in an include. If so, doesn't that mean I will have parsed a lot of class definition code each time I execute a script for things that aren't required on that particular execution? Does PHP handle this well? Perhaps the hit on modern web servers is minimal, and more than offset by the gain in structured, easily-managed applications. (And apologies if I'm using any OOP terms sloppily).