php: is assoc array

is_assoc_array.php

<?php

/**
 * is assoc array
 *
 * @see http://jp.php.net/manual/ja/function.is-array.php
 * @param array $a 
 * @access public
 * @return bool
 */
function is_assoc_array( $a ) {
    return is_array( $a ) && ( count( $a ) !== array_reduce( array_keys( $a ), create_function( '$a, $b', 'return ($b === $a ? $a + 1 : 0);' ), 0 ) );
}