CODEWITHSUNDEEP
phpvariablesreference
linus72982
linus72982

Reputation: 1393

Is there a function like is_reference_of in php?

I'd like to be able to inquire my program as to what variable a variable is a reference of. Is there a way to do this? I looked in all the usual sources and couldn't find anything, perhaps my search terms were goofy. Thanks.

Upvotes: 1

Views: 100

Answers (4)

Headshota
Headshota

Reputation: 21439

you can just compare references with === operator

Note: this only compares object references.

$obj1 = new DateTime();
$obj2 = $obj1;

if($obj2 === $obj1){
    echo "Equal";
}else {
    echo "Not Equal";
}
// Outputs Equal


$obj2 = new DateTime();

if($obj2 === $obj1){
   echo "Equal";
}else {
   echo "Not Equal";
}
// Outputs Not Equal

Upvotes: 3

Matthew
Matthew

Reputation: 48304

As far as I know, there's no direct way to test if two variables point to the same thing. Something like this might work:

function is_reference_of(&$a, &$b)
{
  // if an object, use strict comparison
  if (is_object($a)) return $a === $b;

  // definitely not a reference to each other if they aren't the same value
  if ($a !== $b) return false;

  $tmp = $a;

  if (is_array($a))
  {
    $a = 0;
    // if $b is no longer an array, then it must be a reference to $a
    $is_ref = !is_array($b);
  }
  else
  {
    $a = !$a;
    // if $b is no longer equal to $tmp, then it must be a reference to $a
    $is_ref = ($b !== $tmp);
  }

  // make sure to reset $a back to what it was
  $a = $tmp;

  return $is_ref;
}

$a = 0;
$b = 0;

is_reference_of($a, $b); // false

$b = &$a;

is_reference_of($a, $b); // true

Huge disclaimer: I haven't really thought this through carefully. There could be all sorts of side effects to doing something like the above. Consider this just a proof of concept to get you started

If you are always working with arrays or classes, you could try setting a temporary field or property in one and seeing if it exists in the other, etc. That would be less prone to errors than the above code that changes the entire variable.

Note that the order of the parameters in the above function does not matter.

Update: With objects, you can use === and skip the function altogether. I've updated the function slightly to detect what type of variable is being tested and react accordingly. The disclaimer still applies.

Upvotes: 0

Dan Lugg
Dan Lugg

Reputation: 20612

If you're dealing with objects, I believe === performs the test you want.

$obj1 = new Object;
$obj2 = $obj1;

echo ($obj1 === $obj2) ? 'same' : 'not same'; // same

$obj2 = new Object;

echo ($obj1 === $obj2) ? 'same' : 'not same'; // not same

Upvotes: 0

Jeremy Dentel
Jeremy Dentel

Reputation: 837

The only code I personally know is to directly query what a class is of, not to retrieve it:

if($var instanceof Your_Class) { }

If you know the variable is strictly a class, you can use:

get_class();

If you use the function on a non-object, it appears to return an E_WARNING. I'd suggest code such as this:

$class_known = false;
if(is_object($class))
{
    $class_name = get_class($class);
    $class_known = false;
}

if($class_known)
{
    echo $class_name;
}

Upvotes: 0

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