Question

I read about the class autoloading in PHP, but till now I didn’t understand why we should use __autoload() method?

I read that

PHP doesn’t use
this method becuase it has the handy little include functions,
include_once and require_once, that prevent you from loading the same
file more than once, but unlike a compiled language, PHP re-evaluates
these expressions over and over during the evaluation period each time
a file containing one or more of these expressions is loaded into the
runtime in this site why we should use autoloading,

but I don’t understand what is the meaning of PHP re-evaluates in the above statement!!
why require-once don’t solve the problem of loading php file more than once?

Answer 1

The original article is more clear when you read it more widely (see below) :

It simply says that __autoload() is smarter than include_once() because the function include_once() has to be coded explicitly when the class may be required, and also because this function needs to be processed each time it appears in order to know if the file given in argument is already loaded or not.

The other function __autoload(), on the contrary, can be called only once for several classes you may need. And then PHP tryes to load the corresponding source file only when a class definition is missing.

We can sum up this argumentation by saying: you need one include_once() for each Class/Function source, while only one __autoload() may be enough for a set of Class source having the same location rule.

Snippet of the article:

Why you should use an autoload function in PHP

The loading of classes is something that managed languages like Java
and C# don’t need to worry about, class loaders are built into the
compiler.

 [...]

PHP doesn’t use this method becuase it has the handy little include functions, include_once and require_once, that prevent you
from loading the same file more than once, but unlike a compiled
language, PHP re-evaluates these expressions over and over during the
evaluation period each time a file containing one or more of these
expressions is loaded into the runtime. That is where the Standard PHP
Library (SPL), introduced in PHP 5, and the wonderful little _autoload
function come in to enhance the speed and uniformity of your PHP code.

__autoload is a magic function, that you define, that enables PHP to let you know when it doesn’t have a class loaded, but that class
needs to be loaded.