Is it possible to pass array keys by reference using PHP's native foreach control structure?

Answer: No. However, you can have by ref access to an array's keys using the following code:

<?php
ArrayUtil::ForEachFn($array, function (&$key, &$value) {
    // YOUR CODE HERE
});

To use this technique in your project simply add the following class:

<?php
class ArrayUtil
{
    public static function ForEachFn(Array &$array, $fn)
    {
        $newArray = array();
        foreach ($array as $key => $value)
        {
            $fn($key, $value);
            $newArray[$key] = $value;
        }
        $array = $newArray;
    }
}

To see it all in action checkout the following example:

<?php
// EXAMPLE ARRAY
$array = array(
    'key1' => 'value1',
    'key2' => 'value2',
    'key3' => 'value3',
);

// BEFORE
print_r($array);

// EXAMPLE USAGE
ArrayUtil::ForEachFn($array, function (&$key, &$value) { // NOTE THE FUNCTION'S SIGNATURE (USING & FOR BOTH $key AND $value)
    if ($key === 'key2')
    {
        $key = 'BY REF KEY EXAMPLE'; // THIS IS THE WHOLE POINT OF THIS POST
    }
    if ($value === 'value2')
    {
        $value = 'BY REF VALUE EXAMPLE';
    }
});

// AFTER
print_r($array);

/* THE ABOVE "EXAMPLE USAGE" OUTPUTS:
Array
(
    [key1] => value1
    [key2] => value2
    [key3] => value3
)
Array
(
    [key1] => value1
    [BY REF KEY EXAMPLE] => BY REF VALUE EXAMPLE
    [key3] => value3
)
*/

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