Retrieve the Currently Executing Closure in PHP 8.5

PHP 8.5 will support recursion in Closures by fetching the currently executing Closure (hat tip to Alexandre Daubois). As pointed out in the rfc:closure_self_reference RFC, the current workaround is binding a variable reference into a closure:

$fibonacci = function (int $n) use (&$fibonacci) {
    if ($n === 0) return 0;
    if ($n === 1) return 1;
    return $fibonacci($n-1) + $fibonacci($n-2);
};
 
echo $fibonacci(10). "\n";

Starting in PHP 8.5, you can use the getCurrent() method to fetch the currently executing closure. The code takes a different approach from the original RFC mentioned above—the author dubbed the merged proposal as "a much simpler alternative":

$fibonacci = function (int $n) {
    if (0 === $n || 1 === $n) {
        return $n;
    }
 
    $fn = Closure::getCurrent();
 
    return $fn($n - 1) + $fn($n - 2);
};
 
echo $fibonacci(10) . "\n";

If you're interested in the implementation, check out Pull Request #18167 in the PHP source (see eb65ec4).