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 at least) if this applies to arrays in general.

Here is my try at the array var var.

     // Array Example
     $arrayTest = array('value0', 'value1');
     ${arrayVarTest} = 'arrayTest[1]';
     // This returns the correct 'value1'
     echo $arrayTest[1];
     // This returns null
     echo ${$arrayVarTest};

Here is some simple code to show what I mean by object var var.

     ${OBJVarVar} = 'classObj->obj'; 
     // This should return the values of $classObj->obj but it will return null  
     var_dump(${$OBJVarVar});

Am I missing something obvious here?

Updated my answer to include the array index problem too, I misread you and thought you had that under control! — johnnyArt
– johnnyArt, Commented Jan 10, 2010 at 9:56
If variable-variable is the answer, you are probably asking wrong question. Why not just use by-reference assignment? — Michał Niedźwiedzki
– Michał Niedźwiedzki, Commented Jan 17, 2010 at 11:34

johnnyArt · Accepted Answer · 2010-01-10 10:22:28Z

5

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!

edited Jan 10, 2010 at 10:22

answered Jan 10, 2010 at 9:30

johnnyArt

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1 Comment

K-2052 Over a year ago

Thanks! Exactly what I was trying to accomplish. Worked Perfectly.

Lukman · Accepted Answer · 2010-01-10 09:17:22Z

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;

answered Jan 10, 2010 at 9:17

Lukman

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2 Comments

mauris Over a year ago

asker is not asking about referencing.

hugsbrugs Over a year ago

@mauris : perhaps but finding this answer while googling gave me solution I was looking for ;)

Philippe Gerber · Accepted Answer · 2010-01-10 09:10:22Z

0

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. ;-)

answered Jan 10, 2010 at 9:10

Philippe Gerber

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Comments

mauris · Accepted Answer · 2010-01-10 09:16:06Z

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);

Mostafa Nobaqi · Accepted Answer · 2020-01-14 13:36:03Z

0

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;

answered Jan 14, 2020 at 13:36

Mostafa Nobaqi

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