SPL Throwing Exceptions

Question

Is there a way to throw exceptions from an SPL Autoloader in PHP in case it fails? It doesn't seem to work under PHP 5.2.11.

class SPLAutoLoader{

    public static function autoloadDomain($className) {
        if(file_exists('test/'.$className.'.class.php')){
            require_once('test/'.$className.'.class.php');
            return true;
        }       

        throw new Exception('File not found');
    }

} //end class

//start
spl_autoload_register( array('SPLAutoLoader', 'autoloadDomain') );

try{
    $domain = new foobarDomain();
}catch(Exception $c){
    echo 'File not found';
}

When the above code is called, there is no sign of an exception, instead I get a standard "Fatal error: Class 'foobarDomain' not found in bla". And the execution of the script terminates.

Answer 1

According to the comments in the documentation for spl_autoload_register, it's possible to call another function from the autoloader, which in turn would throw the exception.

class SPLAutoLoader{

    public static function autoloadDomain($className) {
        if(file_exists('test/'.$className.'.class.php')){
            require_once('test/'.$className.'.class.php');
            return true;
        }       
        self::throwFileNotFoundException();
    }

    public static function throwFileNotFoundException()
    {
        throw new Exception('File not found');
    }

} //end class

//start
spl_autoload_register( array('SPLAutoLoader', 'autoloadDomain') );

try{
    $domain = new foobarDomain();
}catch(Exception $c){
    echo 'File not found';
}

Answer 2

This is not a bug, it's a design decision:

Note: Exceptions thrown in __autoload function cannot be caught in the catch block and results in a fatal error.

The reason is that there may be more than one autoload handlers, in which case, you don't want the first handler to throw an Exception and bypass the second handler. You want your second handler to have a chance at autoloading its classes. If you use a library which makes use of the autoloading feature, you don't want it bypassing your autoload handler because they throw Exceptions inside their autoloader.

If you want to check whether or not you can instantiate a class, then use class_exists and pass true as the second argument (or leave it out, true is the default):

if (class_exists('foobarDomain', $autoload = true)) {
    $domain = new foobarDomain();
} else {
    echo 'Class not found';
}