i want my class to reference a large data object

[sneakyimp]

i have a class called gridPartition.

there are many gridPartition objects in my code, each of which represents a division of a large matrix in memory. two different gridPartition objects can refer to TWO DIFFERENT MATRICES in memory so i can't use a static variable for this because that would require that a single matrix object be common to ALL gridPartition objects.

On the other hand, I don't want ot make a bazillion copies of this huge data object because one is attached to each gridPartition object.

how do I need to declare the matrix property of my gridPartition class? i'm vaguely familiar with the & operator, but am confused here.

here's how i create a gridPartition object:

$p = new gridPartition($x0, $xn, $y0, $yn, $matrix);

should that be &$matrix?

and my class might look something like this:

class gridPartition {
  var $x0;
  var $xn;
  var $y0;
  var $yn;
  var $total;

  function gridPartition($x0, $xn, $y0, $yn, $matrix) {
    $this->x0 = $x0;
    $this->xn = $xn;
    $this->y0 = $y0;
    $this->yn = $yn;
    $this->total = 0;

for($x=$x0; $x<$xn; $x++) {
  for($y=$y0; $y<$yn; $y++) {
    $this->total += $matrix[$x][$y];
  } // for y
} // for x
  } // gridPartition()
} // gridPartition

any help is much appreciated.

[laserlight]

Change your function declaration instead:

function gridPartition($x0, $xn, $y0, $yn, &$matrix) {

You might want to read the PHP Manual on references.

[sneakyimp]

I had read this page:
http://www.php.net/manual/en/language.references.whatdo.php

but my eyes started rolling back into my skull when I tried to understand this ambiguous bit:

Note: Not using the & operator causes a copy of the object to be made. If you use $this in the class it will operate on the current instance of the class. The assignment without & will copy the instance (i.e. the object) and $this will operate on the copy, which is not always what is desired. Usually you want to have a single instance to work with, due to performance and memory consumption issues.

there's an example that it refers to but i just can't understand what it's trying to say. I've read all the other 'passing by reference' pages and it looks like the documentation creators have taken a few shortcuts.

AT any rate, it occurred to me today that I'm trying to define $matrix in a function. This same function also creates the gridPartition objects, assigns $matrix (or a reference to it) as a property of the gridPartition object, and then returns an array of gridPartition objects as its result. Given that matrix is created inside my function, what will the gridPartition objects point to outside the scope of my function?

for instance, assuming this class:

class gridPartition {
  var $v;
  var $matrix;

  function gridPartition($v, &$matrix) {
    $this->v = $v;
    $this->matrix = $matrix;
  } // gridPartition()

} // gridPartition

is this ok or is it a bad idea:

// this is a recursive function which passes arrays of gridPartition objects
// back up
function foo($bar) {
  $matrix[0][0] = $bar;
  $matrix[0][1] = $bar*rand();
  // and so on../


  $result = array();
  $result[0] = new gridPartition(5678, $matrix);
  $result[1] = new gridPartition(9012, $matrix);

  $more_results = foo($bar+1);

  foreach($more_results as $r) {
    $result[] = $r;
  }

  return $result;

} // foo()

[sneakyimp]

I think this code mirrors my project and demonstrates my confusion. I've got 42 lines of code and there are 7 references to 'bigvar'. In my real code, bigvar corresponds to a large data object and the recursive function that creates bigvar is supposed to assign it by reference to not just one but hundreds or thousands of class objects which are in turn bubbled up thru recursion to the top-level of my code. I just can't afford for PHP to be making copies of it bigvar!

WHERE DO I NEED TO PUT THE REFERENCE OPERATORS (&) ??? As I mentioned before there are 7 difference places where 'bigvar' gets referenced in the code. I have taken a few guesses but no luck - the output of the final print_r statement has the array of md5 values rather than the string I change it to in the 7th reference.

Here is the class which refers to bigvar 3 times:

<?php
class testClass {
  var $v;
  var $bigvar; // Ref #1

  function testClass($v, &$bigvar) { // Ref #2
    $this->v = $v;
    $this->bigvar = $bigvar;  // Ref #3
  }

}
?>

and here is the script that uses the class. note how i attempt to change the contents of bigvar after it is assigned to see if the reference is working:

<?
include('classes/testClass.php');

$global_array = array();
$global_array = someFunc(5);
print_r($global_array);

function someFunc($depth) {
  $v = 'md5(' . $depth . ')=' . md5($depth);

  $bigvar = array(); // Ref #4
  for($i=0; $i<10; $i++) {
    $bigvar[$i] = md5($depth); // Ref #5
  }

  $r = new testClass($v, &$bigvar);  // Ref #6

  $bigvar = 'i changed this within someFunc after assigning it to the testClass object'; // Ref #7

  $new_depth = $depth - 1;
  if ($new_depth == 0) {
    return array($r);
  } else {
    $result = someFunc($depth-1); // returns an array
    array_unshift($result, $r);
    return $result;
  }
}
?>