Modify multiple variables with single function in PHP

Question

I need to modify some variables in the same way. For example I need to multiply each variable with 2 when some conditions met. Like this:

$a = 10;
$b = 100;
$c = 1000;
$d = 10000;

if($someCondition) {
    $a *= 2;
    $b *= 2;
    $c *= 2;
    $d *= 2;
}

Here I want to call a function to apply the change to all variables instead of multiplying one by one. I tried using a callback function like this (writing such function for this type of simple calculations may look silly, but I have more complex things to do, just keeping it simple here for better understanding):

Trial 1

function multiply_vars(&$a,&$b,&$c,&$d) {
    foreach(func_get_args() as $val) {        
        $val *= 2;
    }
}

if($someCondition) {
    multiply_vars($a,$b,$c,$d);
}

This works, but I need to know exactly how many variables I am passing to the function and set each variable as reference with &. For example, the above function will give me incorrect result when I pass 5 variables to modify.

Trial 2

function multiply_vars() {
    foreach(func_get_args() as $varname) {
        global $$varname;
        $$varname *= 2;
    }
}

if($someCondition) {
    modify_vars('a','b','c','d');
}

This works in a global context. But the problem is, I am doing this inside a class function where global $$varname refers to a variable outside my class function.

Is there any other way for achieving my purpose?

Note: I don't want to put my variables into an array. I know, it can be better solved by array_map() function, if it was in an array.

Answer 1

You want a variadic argument list
Here's an example of passing a variable number of arguments to a function by reference:
PHP: variable-length argument list by reference?

Copied and Pasted from the above link:

Example 1:

function foo(&...$args) {
    $args[0] = 'bar';
}
foo($a);
echo $a, "\n";
#  output:
#a

Example 2:

function number(&...$args) {
    foreach ($args as $k => &$v) {
        $v = $k;
    }
}
number($zero, $one, $two);
echo "$zero, $one, $two\n";
#  output:
#0, 1, 2

Answer 2

I realize that you said you do not want to put the variables in an array. However, you could potentially pass an array of references to avoid the additional value copy. E.g.

<?php
$a = 10;
$b = 100;
$c = 1000;
$d = 10000;

function multiply_vars($args) {
    foreach($args as &$arg) $arg *= 2;
}

multiply_vars([&$a, &$b, &$c, &$d]);

However, if you're using PHP 5.6 I think Magical Gordon's updated answer is a better solution.

Answer 3

I'd just pass them in as an array. For example:

$variables = array(
    'a' => 10,
    'b' => 100,
    'c' => 100,
    'd' => 1000,
);

function multiply_vars($variables) {
    $returnValues = array();
    foreach($variables as $key => $value) {        
        $newValue = $value * 2;
        array_push($returnValues, array($key => $newValue));
    }
    return $returnValues;
}

if($someCondition) {
    $variablesWithNewValues = multiply_vars($variables);
    //do stuff with  $variablesWithNewValues
}

Answer 4

Your need tells that your strategy is not correct. And even if it worked, your code readability and maintenability will not be good! Anyway, I suggest that you create a function instead of your procedure, which you may call whenever needed and replace the original variable with the output.

An Example:

Function doStuff ($input){
    treat_input;
    Return output;
 }

$x = doStuff ($×);
 ....

Well, I know you will need to call this function as many times as number of variables you have. But trust me, this is the way that you have to go according to long experience in maintaining scripts.

Answer 5

Expanding on the other answers here, why not use an object? I'm assuming your question is a simplistic case, but there are a few benefits: objects are always passed by-reference, and the values assigned to an object's properties can be themselves accessed by-reference.

For example:

$numbers = new \StdClass();
$numbers->a = 10;
$numbers->b = 100;
$numbers->c = 100;
$numbers->d = 100;

You'd then use $numbers->a instead of $a in the global scope -- or use another variable by reference $a = &$numbers->a;

function multiply(StdClass $numbers, $multiple = 2)
{
    // Iteration isn't directly achievable with StdClass but...
    foreach (get_object_vars($numbers) as $key => $value) {
        $numbers->$key *= $multiple;
    }
}

And finally, our conditional:

if (true === myCondition) {
    multiply($numbers);
}