Simple implementation of Rails' .to_sentence for PHP

to_sentence.php

<?php

class ArrayExtensions
{
    public function to_sentence($array) 
    {
        $count = count($array);
        switch ($count)
        {
            case 0:
                $str = '';
                break;
            case 1:
                $str = $array[0];
                break;
            case 2: 
                $str = $array[0].' and '.$array[1];
                break;
            default:
                $str = implode(', ', array_slice($array, 0, -1)).' and '.$array[($count - 1)];
                break;
        }
        
        return $str;
    }
}

This is actually buggy:
$array[($count - 1)]

Should be $count - 2 or simply end($array)