<?php
// Test this online on http://phptester.net/

echo '<pre>';

echo "1. Passing variable by value.\n";

$var1 = 'foo'; // define it
$func = function() use ( $var1 ){
    echo "$var1\n";
};

$func(); // outputs 'foo'
$var1 = 'bar'; // change the value
$func(); // still outputs 'foo'


echo "\n2. Passing variable by reference.\n";

$var2 = 'abc'; // define it
$func = function() use ( &$var2 ){
    echo "$var2\n";
    $var2 = 'def'; // change the value
};

$func(); // outputs 'abc'
echo "$var2\n"; // outputs 'def'
$var2 = '123'; // change the value
$func(); // outputs '123'
echo "$var2\n"; // outputs 'def'

echo '</pre>';