Variable Variables Pointing to Arrays or Nested Objects

Question

Is it possible to create a variable variable pointing to an array or to nested objects? The php docs specifically say you cannot point to SuperGlobals but its unclear (to me

Answer 1

there is a dynamic approach for to many nested levels:

$attrs = ['level1', 'levelt', 'level3',...];
$finalAttr = $myObject;
foreach ($attrs as $attr) {
    $finalAttr = $finalAttr->$attr;
}
return $finalAttr;

Answer 2

Array element approach:

• Extract array name from the string and store it in $arrayName.
• Extract array index from the string and store it in $arrayIndex.
• Parse them correctly instead of as a whole.

The code:

$arrayTest  = array('value0', 'value1');
$variableArrayElement = 'arrayTest[1]';
$arrayName  = substr($variableArrayElement,0,strpos($variableArrayElement,'['));
$arrayIndex = preg_replace('/[^\d\s]/', '',$variableArrayElement);

// This returns the correct 'value1'
echo ${$arrayName}[$arrayIndex];

Object properties approach:

• Explode the string containing the class and property you want to access by its delimiter (->).
• Assign those two variables to $class and $property.
• Parse them separately instead of as a whole on var_dump()

The code:

$variableObjectProperty = "classObj->obj";
list($class,$property)  = explode("->",$variableObjectProperty);

// This now return the values of $classObj->obj
var_dump(${$class}->{$property});    

It works!

Answer 3

Use = & to assign by reference:

 $arrayTest = array('value0', 'value1');
 $arrayVarTest = &$arrayTest[1];

 $arrayTest[1] = 'newvalue1'; // to test if it's really passed by reference

 print $arrayVarTest;

Answer 4

Nope you can't do that. You can only do that with variable, object and function names.

Example:

 $objvar = 'classObj';
 var_dump(${$OBJVarVar}->var);

Alternatives can be via eval() or by doing pre-processing.

$arrayTest = array('value0', 'value1');
$arrayVarTest = 'arrayTest[1]';

echo eval('return $'.$arrayVarTest.';');
eval('echo $'.$arrayVarTest.';');

That is if you're very sure of what's going to be the input.

By pre-processing:

function varvar($str){
  if(strpos($str,'->') !== false){
    $parts = explode('->',$str);
    global ${$parts[0]};
    return $parts[0]->$parts[1];
  }elseif(strpos($str,'[') !== false && strpos($str,']') !== false){
    $parts = explode('[',$str);
    global ${$parts[0]};
    $parts[1] = substr($parts[1],0,strlen($parts[1])-1);
    return ${$parts[0]}[$parts[1]];
  }else{
    return false;
  }
}

$arrayTest = array('value0', 'value1');
$test = 'arrayTest[1]';
echo varvar($test);

Answer 5

In echo $arrayTest[1]; the vars name is $arrayTest with an array index of 1, and not $arrayTest[1]. The brackets are PHP "keywords". Same with the method notation and the -> operator. So you'll need to split up.

// bla[1]
$arr = 'bla';
$idx = 1;
echo $arr[$idx];

// foo->bar
$obj = 'foo';
$method = 'bar';
echo $obj->$method;

What you want to do sounds more like evaluating PHP code (eval()). But remember: eval is evil. ;-)