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PHP: Update global reference variabele inside function scrope

I’m trying to change a global value that is currently a reference to another value. My current implementation doesn’t work:

$anna = array('Name' => "Anna");
$bella = array('Name' => "Bella");
$girl = &$anna;

function change(){
    global $girl, $bella;
    $girl = &$bella;
    // $girl['Name'] is now 'Bella'
    output_girl(); // This still outputs 'Anna'
}

function output_girl(){
    global $girl;
    echo $girl['Name'];
}

change();

// What do we want to see?
echo $anna['Name']; // Should still be 'Anna'
echo $bella['Name']; // Should still be 'Bella'
echo $girl['Name']; // Should now be 'Bella' (in above example this will still be 'Anna')

Important notes:

  • A workaround with a return value like $girl = &change(); is not a solution to my problem. It’s important that the global $girl is changed before the end of the change() function. (Reason being this is a problem inside a complex project with nested function calls all wanting to use the same global variables.)
  • I am aware a workaround could be coded using the $GLOBALS array. However, I am specifically interested if this problem can be solved using the global keyword as seen in the example code. And if not, to know why this isn’t possible in PHP.
  • Removing the &to make it $girl = $bella is also not a solution. The global $girl object needs to always be a reference to the original arrays defined at the start of the script. We cannot ever make copies / break references.

Question: Is this an impossibility in PHP when I use the global keyword? If so, can someone explain why? If not, can someone explain how to make this work?

Tags:

2

Answers


  1. 0

    It’s impossible to do that in PHP with only global keyword.

    This is because references in php are not same as pointers as we know them for example from C/C++.

    When you do $girl = &$anna; on line 3 it doesn’t store address of $anna variable in $girl variable. Rather the new symbol $girl is created to reference same variable as symbol $anna.

    When you do global $girl, $bella; inside of a function. New local symbols $girl and $bella are created and they are made to reference their global counterpart.

    When you do $girl = &$bella; inside the function the local symbol $girl is changed to reference same variable as local symbol $bella but the global symbol $girl is not changed. After doing that both local symbols $girl and $bella are referencing same global symbol $bella.

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  2. 0

    The problem is that your global is still referencing to $anna.

    you can check it by adding print_r($GLOBALS[‘girl’]):

    function change(){
    global $girl, $bella;
    $girl = &$bella;
    print_r($girl); //referencing to bella
    print_r($GLOBALS['girl']); //referencing to Anna
    output_girl(); // This still outputs 'Anna'
}

    }

    I don’t know the correct solution for this, but there is a way around it. Just add:

    function change(){
    global $girl, $bella;
    $GLOBALS['girl'] = &$bella;
    output_girl(); // now is 'Bella'
}
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