PHP Pass by reference confusion

Question

To cut a long story short I have the following function as part of my framework:

public function use_parameters()
{
    $parameters = func_get_args();

    $stack = debug_backtrace();

    foreach($stack[0]['args'] as $key => &$parameter)
    {
        $parameter = array_shift($this->parameter_values);
    }
}

Where $this->parameter_values = array('value1', 'value2', 'value3', 'value4', 'value5', ...);

Which is used in the following context:

$instance->use_parameters(&$foo, &$bah);

Assigning:

$foo = 'value1';
$bah = 'value2';

Calling it again

$instance->use_parameters(&$something); 

Will set

$something = 'value3'

and so on.

As of 5.3 it would return a 'Deprecated: Call-time pass-by-reference has been deprecated' warning. In an effort to conform to the 5.3 way of working I removed the &'s resulting in:

$instance->use_parameters($foo, $bah);

This unfortunately has caused the arguments not to be set and I'm struggling to come up with a solution.

For what its worth I'm running PHP v5.3.3-7 on Apache/2.2.16 (Debian)

Any help would be greatly appreciated.

Answer 1

You can't do that in PHP and you are abusing the concept of references. You have to specify the reference arguments explicitly, albeit with default values. However , you don't want to use NULL as a default as this is what an unassigned reference variable will be set to. So you need to define some constant that you know is not going to be used as a parameter, and now the code will look something like

    const dummy="^^missing^^";

    public function use_parameters(&$a, &$b=self::dummy, &$c=self::dummy ) {
        $a=array_shift($this->parameter_values);
        if($b!==self::dummy) $b=array_shift($this->parameter_values);
        if($c!==self::dummy) $c=array_shift($this->parameter_values);
        # add $d,$e,$f,... as required to a sensible max number
    }

Note that because you are using references properly, you don't need the debug_backtrace() botch.

Answer 2

You can't do that in PHP 5 or ... as you've seen you can, but it's deprecated and raises warnings. You'll have to either have a predefined max count of function arguments or use an array:

public function use_parameters(&$arg1, &$arg2 = NULL, &$arg3 = NULL)
{
    // if ($arg2 !== NULL)
    // if ($arg3 !== NULL)
}

$parameters = array(0 => &$foo, 1 => &$bah);

public function use_parameters($args)
{
    // Handle the array elements
}