How to decrease memory usage when passing big variables around

Question

For example:

a(wordwrap(str_repeat('abcdef', 500000), 160, "\n", true));    

function a($v){
  $v[1] = 'x';      
  $v = b($v);
  return $v;
}

function b($v){
  $v[2] = 'x';    
  $v = c($v);
  return $v;
}

function c($v){
  $v[3] = 'x';  
  d($v);    
}

function d($v){
  $v[4] = 'x';
  print $v;
}

This uses ~23 MB. I think because PHP is creating a copy of that text on each modification. If I just print the text once it uses 12 MB.

Can I somehow free the memory for the original variable before functions are called? Like

unset($v);
$v = c($v);

Obviously this won't work because $v is destroyed before it gets passed to c() lol. But I'd like to somehow let c() modify the same text. Like using references. (I tried references but they actually increase memory usage, probably because PHP makes more copies)

Answer 1

Yes, you are right, PHP uses copy-on-write approach. You might wanna try references, e.g.:

function a(&$v){
    $v[1] = 'x';      
    $v = b($v);
    return $v;
}

I just noticed, that you tried references, are you sure that memory usage wasn't lower?