Higher order capture

capture.php

<?php
class Connection
{
    public function transactional(callable $callback)
    {
        $callback();
    }
}

function capture(&$result, callable $callback) {
    return function () use (&$result, $callback) {
        $result = $callback();
    };
}

$connection = new Connection();
$connection->transactional(capture($result, function() { return 'hello';}));

var_dump($result);