When do I use static variables/functions in php?

Question

I am refreshing myself on OOP with PHP and I saw an example of setting functions and/or variables as static. When and why would I set a variable/function to static? I\'ve

Answer 1

Here's a random, though fairly good description of the differences between static and instance methods.

From the post:

Instance methods are instance methods because they rely on the state of the specific object instance. Instance methods are tied to a particular instance because the behavior that the method invokes relies upon the state of that particular instance.

When you declare a method as static, you define that method as being a class method. A class method applies to the class as opposed to any particular instance. The behavior instigated by a class method does not rely on the state of a particular instance. In fact, a static method cannot rely on an instance's state since static methods lack access to this reference. Instead, the behavior of a class method either depends on a state that all objects share at the class level, or is independent of any state at all.

If a method relies on an object instance's state it should be an instance methods. If a method is general for all or no instances of a class, and does not rely on the object state, it should be a static method. Instance methods are most commonly used. However static methods are very useful for utility and factory classes amogst many other uses.