Make a multidimensional array with keys from a string with a variable amount of key names placed between square brackets

m_array_keys_from_string.php

<?php
/**
 * Problem:
 * Given a string similar to '[key][subkey][otherkey]' 
 * we want to make a multidimensional array $array['key']['subkey']['otherkey']
 * 
 * Original question on Stackoverflow:
 * @link http://stackoverflow.com/questions/31103719/php-make-a-multidimensional-associative-array-from-key-names-in-a-string-separat/31104168
 * There are alternative solutions posted.
 */

$str = '[key][subkey][otherkey]';
$value = 'my_value';
$arr = [];

// Note: a different approach would be using explode() instead
preg_match_all( '/\[([^\]]*)\]/', $str, $has_keys, PREG_PATTERN_ORDER );

if ( isset( $has_keys[1] ) ) {

  $keys = $has_keys[1];
  $k = count( $keys );
  if ( $k > 1 ) {
    for ( $i=0; $i<$k-1; $i++ ) {
      $arr[$keys[$i]] = walk_keys( $keys, $i+1, $value );
    } 
  } else {
    $arr[$keys[0]] = $value;
  }

  $arr = array_slice( $arr, 0, 1 );

}

var_dump( $arr );

function walk_keys( $keys, $i, $value ) {
  $a = '';
  if ( isset( $keys[$i+1] ) ) {
     $a[$keys[$i]] = walk_keys( $keys, $i+1, $value );
  } else { 
     $a[$keys[$i]] = $value;
  }
  return $a;
}