PHP RFC: Closure self reference


Currently, the main way used to call a closure from within that closure, is to bind a variable by reference into the closure, when the closure is created.

However this can lead to shenanigans:

$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";
$this_is_the_original_fibonacci = $fibonacci;
// ... many lines of code here
$fibonacci = function (int $n) { return rand(0, $n); };
// ... many lines of code here
echo $this_is_the_original_fibonacci(10). "\n";

i.e. a change to the variable outside the closure has modified the behaviour of the closure. That a closure can change behaviour like this violates the Principle of least astonishment


Allow closures to be aliased to a variable that can be used within the closure:

$fibonacci = function (int $n) as $fibonacci {
    if ($n === 0) return 0;
    if ($n === 1) return 1;
    return $fibonacci($n-1) + $fibonacci($n-2);

Backward Incompatible Changes

None known.

Proposed PHP Versions


RFC Impact

To Opcache


Future Scope


Proposed Voting Choices

Accept this RFC and make it possible to reference a closure from within itself using `as $variable` ? Yes/no.

Patches and Tests

Links to any external patches and tests go here.


None yet.


Links to external references, discussions or RFCs

Rejected Features

Keep this updated with features that were discussed on the mail lists.

rfc/closure_self_reference.txt · Last modified: 2020/11/18 21:30 by danack