PHP, Closures, use & references

I want to talk about one feature of using closures in PHP-5.3. I think for many it will seem obvious, but nonetheless. It turns out using use ($ var1, ..) - we can pass variables by reference: use (& $ var1, ..).

An example illustrating possible use cases (and please do not poke your nose into array_sum () ;)):

$ rows = array (1, 2, 3);
$ total = 0;
// Case of times - use ($ total) without reference
array_walk ($ rows, function ($ row) use ($ total) {
        $ total + = $ row;
});
echo "Total is $ total \ n";
// Case two - use (& $ total) by reference
array_walk ($ rows, function ($ row) use (& $ total) {
        $ total + = $ row;
});
echo "Total is $ total \ n";

At the output we get:

Total is 0
Total is 6

Enjoy!