CHAPTER 2 ■ FOUNDATION
12
{
autoload($class);
}
}
spl_autoload_register('autoload');
spl_autoload_register(array('autoloader', 'autoload'));
// these can only be called within a class context…
// spl_autoload_register(array($this, 'autoload'));
// spl_autoload_register(__CLASS__.'::load');
e rst call to spl_autoload_register() tells PHP to use the autoload() method to load a class le by
name. e second call to spl_autoload_register() tells PHP to use the Autoloader::autoload() method to
load a class le by name. e third and fourth calls to spl_autoload_register() tell PHP to use the autoload()
method, belonging to the class in which these spl_autoload_register() calls occur, to load a class le by name.
e autoload() function rst splits the returned string of PHP’s get_include_path() function into separate
directories. It then constructs the target le name by splitting the requested class name on the second, third,
fourth, and so on, uppercase letters and joining the words together using the PATH_SEPARATOR constant.
If it nds the target le within any of the $paths directories, it will include the le and end function
execution with a return statement. If the le is not found by the end of the loop, through $paths, an Exception
will be thrown. If no exception is thrown, you can assume that a le matching the class name was found (in one
of the directories in the include path) and was included successfully.
Note
■ If you would like to know more about PHP namespaces, you can see the full documentation (and some
examples) at http://php.net/manual/en/language.namespaces.php.
Exceptions
One of the ways in which PHP deals with special conditions that change the normal ow of a program
(e.g., runtime errors) is to raise exceptions. Along with the built-in Exception class, PHP also has a mechanism
of detecting that an Exception has occurred, and doing something useful when it does. Listing 2-4 shows an
example.
Listing 2-4. Try/Catch Control Flow Statement
try
{
throw new Exception();
}
catch (Exception $e)
{
echo "An exception was raised.";
}
roughout this book, we will see code that deals with a wide range of Exception subclasses. Most of those
subclasses we will make ourselves, though they will be subclasses of those found in the SPL. You might be
wondering why we would ever need to subclass Exception (or any of the SPL Exception subclasses) if we can just
try/catch Exception to deal with errors in our framework, as shown in Listing 2-5.
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