在PHP中判断单个字符是否为字母数字的最有效方法是什么？

What's the most efficient way to tell if a single character is alphanumeric in PHP?

I know I could do something like:

function isSingleAlphaNum($chr){
    if(!is_string($chr){
        return false;
    }

    //capture the first alphanumeric character, replace the whole string with it
    $test = preg_replace('#([a-zA-Z0-9]{1}).*#','$1',$chr);
    if($test == $chr){
        return true;
    }

    return false;

}

This seems clunky. Is there a better way?

Good 'ol ctype_alnum() http://www.php.net/manual/en/function.ctype-alnum.php

ctype_alnum($chr); 

What about ctype-alnum?