calling a class

[Xdega]

This is probably a quick one. I am pretty new to OOP, in fact somewhat a novice. I am working a lot more with objects lately as my previous "flat" php experience doesn't allow me to create clean and expandable applications. Of course though, questions will always pop up (that's what you guys are for?)

 

One concept I am having trouble understanding, is the method to call a class.

 

What is the difference between?:

 

<?php $cat = new class(); ?>

 

and just simply:

 

<?php  new class(); ?>

 

Both appear to have the same output from my small amount of practice, but the first way seems strange to me. Being that I am very new to OO PHP, the first way looks like it is just defining a var. But in reality it is calling the class and running it? This seems very backwards to me and I am having a hell of a time understanding it. I am aware that the first way seems to be the "proper" way, but just can't fathom it.

 

Could someone explain this to me a little further?

thanks much,

[KevinM1]

A constructor is a function/method with an implicit return value - an object of that class.  In order to capture and handle this new object, it needs to be stored in a variable, else it'll be inaccessible.  It's no different than any other function that returns a value, with the exception that an explicit return statement isn't used.  For that reason, version 1 is the way to go and version 2, while technically syntactically correct as well, is useless.

[Xdega]

see my confusion here is that :

$cat = new class(); 

although the above is storing the return value (I think I understand that now), it still executes the code contained in the class without you telling it to?

 

[KevinM1]

A class doesn't 'run'.  A class is a blueprint for a custom type.  An object is an instance of that class*.  To create a new object, a special method known as a constructor is executed.  A constructor is ALWAYS executed, regardless of whether or not you define one in your class.  If you don't define one, PHP's default constructor is executed.  All this does is inform the interpreter that a new object of that type now exists.

 

*A type is generally described as data which adheres to certain criteria and the actions that can work on that data.  An example would be integers.  They represent data of a certain criteria (whole numbers) and allow certain actions to work on that data (mathematical operations).  An instance of an integer would be 4.

[KevinM1]

The functions/methods defined in a class are only invoked when an object explicitly invokes them.  They don't automatically run in sequence when you call for a new object.

[Xdega]

Well thanks for that. I know that teaching OOP concepts can be as hard as figuring them out. I think I understand a little better now though.

Thanks again. Also off topic, your sig link looks rather interesting Having used w3schools a lot.