Question

I have never used anonymous functions in PHP before, but I found a piece of code that uses one in order to sort objects

usort($numTurnsPerUser,build_sorter('turns'));

function build_sorter($key) {
    return function ($a, $b) use ($key) {
        return strnatcmp($a[$key], $b[$key]);
    };
}

This code will sort an object by a key (I pass in “turns”). For example, an object that looks like this: (written in JSON, just for readability)

$numTurnsPerUser = {
    "31":{
        "turns":15,
        "order":0
    }, "36":{
        "turns":12, 
        "order":1
    }, "37":{
        "turns":14, 
        "order":2
    }
}

will be sorted into an object that looks like this:

$numTurnsPerUser = {
    "36":{
        "turns":12,
        "order":1
    }, "37":{
        "turns":14,
        "order":2
    }, "31":{
        "turns":15, 
        "order":0
    }
}

This worked great on my local server, which is running PHP 5.3.0, but it fails to work on my online server, which is running “php5” – I’m unable to find any information other than that. I am getting an error

Parse error: syntax error, unexpected T_FUNCTION

I read that PHP < 5.3 cannot use anonymous functions and must use create_function, but the “use” part of the anonymous function has me stumped. Could someone please explain to me what that “use” part of the function is, or better yet, how I can “translate” this to the create_function parameters needed?

Answer 1

You could do like this:

Class Sorter {
  private $key;

  public function __construct($key) {
    $this->key = $key;
  }

  public function sort($a, $b) {
    return strnatcmp($a[$this->key], $b[$this->key]);
  }
}

usort($numTurnsPerUser, array(new Sorter('key_b'), 'sort'));