PHP array as variable name

Not in one go like that. Here's how you'd do it:

$array['Something']['More']['id']

If you particularly wanted access multidimensional arrays with a single string, then you could build a function to do that:

function array_multi(Array $arr, $path) {
    $parts = explode(".", $path);

    $curr =& $arr;
    for ($i = 0, $l = count($parts); $i < $l; ++$i) {
        if (!isset($curr[$parts[$i]])) {
            // path doesn't exist
            return null;
        } else if (($i < $l - 1) && !is_array($curr[$parts[$i]]) {
            // path doesn't exist
            return null;
        }
        $curr =& $curr[$parts[$i]];
    }
    return $curr;
}

// usage:
echo array_multi($array, "Something.More.id");    // 34
echo array_multi($array, "Something.More");       // array("id" => 34)

Recursive version supporting your syntax with square brackets:

$array = array('Something'=>array('More'=>array('id'=> 34)));

$string = '[Something][More][id]';

echo scan_array($string, $array);

function scan_array($string, $array) {
    list($key, $rest) = preg_split('/[[\]]/', $string, 2, PREG_SPLIT_NO_EMPTY);
    if ( $key && $rest ) {
        return scan_array($rest, $array[$key]);
    } elseif ( $key ) {
        return $array[$key];
    } else {
        return FALSE;
    }
}

Ok, I know this is how people get shot. But c'mon, eval() is not always the wrong answer.

$array = array('Something'=>array('More'=>array('id'=> 34)));
$index_name = '[Something][More][id]';
eval('$val = $array'.$index_name.';'); // Wrap in a function or something

You could do this with eval():

<?php

$array = array('Somthing'=>array('More'=>array('id'=> 34)));
$index_name = "['Somthing']['More']['id']";

$stmt='echo $array'.$index_name.';';
eval($stmt);

?>

UPDATE:

It seems some SO users are uncomfortable with the idea of using eval(). I think it makes sense to read this thread which discusses the pros and cons before deciding whether to use this in your own code.

If you've cornered yourself into needing to do something like this, there's a pretty good chance you've done something else in a poor way. There's valid reasons to do this, but not very often.

function key_path($arr, $keys) {
    return $keys ? key_path($arr[array_shift($keys)], $keys) : $arr;
}

$arr['Something']['More']['id'] = 34;
$keys = array('Something', 'More', 'id');

var_dump( key_path($arr, $keys));