In PHP, what are magic methods and how are they used?

Question

I have been looking at my copy of the php manual, at magic constants and have a question about two of them.

1: __line__ : I presume that this would be irrelevant if a script file was compressed by removing all the superfluous white space, including line breaks and tabs? (Although since php is not exposed to the client unless the developer uses highlight_file or highlight_string, compressing it this way is not too useful)

2: __trait__: This is the first time I have run into this term in a programming context. What does it mean? In the manual there is an associative reference to namespace. Perhaps I should read up on namespaces relative to php. The only other context I am aware of the term is in XML This is a bit confusing because I have seen the term used referring to object/property relationships, such as in javascript.

Specifically, you can create an object through the use of a constructor function

function SomeJSObj()
 {
   this.introduce = function(a)
   {
    alert('Hi, I am '+a)
   }
 }

var guy = new SomeJSObj()

guy.introduce('Max') // -> alert dialog -> "Hi, I am Max"

So the function/property 'introduce' is namespaced by the object guy.

So, how is it different than a member function or variable of a class that can only be accessed via reference to an object instance?

Then, finally, how does the term inferred by __trait__ relate?

Answer 1

PHP functions that start with a double underscore – a “__” – are called magic functions (and/or methods) in PHP. They are functions that are always defined inside classes, and are not stand-alone (outside of classes) functions.

The magic functions available in PHP are:

__construct(), 
__destruct(), 
__call(), 
__callStatic(), 
__get(), 
__set(), 
__isset(),
 __unset(), 
__sleep(), 
__wakeup(), 
__toString(), 
__invoke(), 
__set_state(), 
__clone(),
and 
__autoload().