Question

I can change $var in my function in one of two ways: either pass it by reference or using the global keyword.

$var1 = 10;

function test1() {
    global $var1;
    $var1++;
}

function test2(&$var) {
    $var++;
}

Both approaches have the same result, but is there any difference between them? Which one is preferred and which one is faster?

Answer 1

1. None of them is preferred.

Unless you have a special reason to do otherwise, the preferred would be

$var1 = 10;
$var1 = test3($var1);
function test3($var)
{
    return $var + 1;
}

Introducing coupling between different parts of your program (if using a global) is something you should always reasonably try to avoid.

In addition, if there is no concrete reason to make your function accept its argument by reference you should also avoid doing that. Only a very miniscule fraction of all functions behave this way, so if nothing else you are risking confusion among the developers who use this code for no real benefit.

2. You do not need to think about which one is faster.

Unless you have profiled your application under real world scenarios and have found that this function is a bottleneck (which of course it will never be in this simple form), then optimizing for performance at the expense of writing clear and maintainable code is not only pointless, but also detrimental.

As a bonus, I should mention that using a reference might actually make the function slower.