PHP RFC: Closure self reference

• Version: 0.2
• Date: 2020-11-10
• Author: Danack
• Status: Draft
• First Published at: https://wiki.php.net/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);
};

None known.

8.1

Unknown.

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

Links to any external patches and tests go here.

None yet.

Links to external references, discussions or RFCs

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