PHPBuilder - Object Oriented Programming in PHP: The Way to Large PHP Projects Page 4

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Object Oriented Programming in PHP: The Way to Large PHP Projects - Page 4

by: Luis Argerich
January 25, 2008

When an object of a derived class is created only its constructor is called, the constructor of the Parent class is not called, this is a gotcha of PHP because constructor chaining is a classic feature of OOP, if you want to call the base class constructor you have to do it explicitely from the derived class constructor.It works because all methods of the parent class are available at the derived class due to inheritance.


function Another() {
$this->Something();   //explicit call to base class constructor.

A nice mechanism in OOP is to use Abstract Classes, abstract classes are classes that are not instanciable and has the only purpose to define an interface for its derived classes. Designers often use Abstract classes to force programmers to derive classes from certain base classes so they can be certain that the new classes have some desired functionality. There's no standard way to do that in PHP but:
If you do need this feature define the base class and put a "die" call in its constructor so you can be sure that the base class is not instanciable, now define the methods (interface) putting "die" statements in each one, so if in a derived class a programmer doesn't override the method then an error raises. Furthermore you might need to be sure since php has no types that some object is from a class derived from you base class, then add a method in the base class to identify the class (return "some id"), and verify this when you receive an object as an argument. Of course this doesn't work if the evil programmer oveerides the method in the derived class but genrally the problem is dealing with lazy programmers no evil ones! Of course is better to keep the base class unreachable from the programmers, just print the interface and make them work!
There're no destructors in PHP.

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