I read the answer to this question but it led to more questions: PHP variables reference and memory usage
In short, I have a project where I'm trying to loop through a multidimensional array to grab one value before continuing on with either the process or the loop. It'll be easier to explain in code:
// Demo variables
$this->content['alias1'] = ('object' => new someObject; 'info' => array('type' => 'abc'));
$this->content['alias2'] = ('object' => new someObject; 'info' => array('type' => 'def'));
$this->content['alias3'] = ('object' => new someObject; 'info' => array('type' => 'abc'));
... that's incredibly simplified, but it gets the point across. I want to loop through that and find all of the 'types' that are 'abc' - what's the easiest way to do it? I had something like this
foreach($this->content as $alias => $data) {
if ($data['info'] != 'abc') {
break;
}
// Do actual "abc" things
}
But I'm trying to write all of this code as memory-conscientious as I can. I feel as though there's probably a more efficient way to do this.
I was thinking that when the objects are loaded (this is essentially a config file), it would assign a reference to another variable, something like
$this->types->$type =& $this->content['alias1'];
for each. In the question referenced above, it said that PHP uses copy-on-write with references - if the reference is only read, never written, would this be an efficient way to be able to access the object? I was also thinking that maybe I could just store the array key name in the $this->types->$type array.
Copy-on-write means that PHP will automatically create a reference for you, provided you don't write to the target variable. If you write, it will copy the original value, and modify the copy instead. Bottom line is: you don't need to manually assign by reference in this case, you can just use a regular assignment:
$this->types->$type = $this->content['alias1'];
As long as you're just reading from $this->types->$type, it will be pointing to the same value in memory as $this->content['alias1'].
PHP does copy on write for most of variables you pass around as arguments. Anyways, that's what my experiments led me to believe (even if you can break this in special cases). So, if you just need to loop and you don't play with references and such... you'll be safe.
But there's a way to check. Using the following 2 functions:
Use these two functions inside your code and check how your memory consumption changes as your code execution advances. This way, no matter what funky things you do with PHP, you'll easily tell if PHP is still doing copy-on-write or has done the copy for you.