RFC: Support for multi-line arrow functions

Hey internals, A few days ago I opened a pull request that adds support for multi-line arrow functions in PHP: https://github.com/php/php-src/pull/6246. As you may already know, PHP 7.4 has introduced one-liner arrow functions (aka short closures). Now, this pull request adds the possibility of those arrow functions to be multi-line. Just like in Javascript, or Hack. Let's see an example: ```php $users = [/** */]; $guestsIds = [/** */]; $repository = /** */; $guests = array_filter($users, fn ($user) => { $guest = $repository->findByUserId($user->id); return $guest !== null && in_array($guest->id, $guestsIds); }); ``` In short, the advantages are: ``` $values = array_filter($values, function ($value) use ($first, $second, $third) { // vs $values = array_filter($values, fn ($value) => { ``` - Multi-line arrow functions don't require the use keyword to be able to access data from the outer scope. - Also, in some cases, fn (/** */) => { is just shorter and simpler than function (/** */) use (/** */) {. This pull request has been very well received by the community on Github, and also on Twitter: https://twitter.com/enunomaduro/status/1311572174256340992. So, I am writing this email to get your feedback about having this feature in the core of PHP. Note that, if eventually, you think it is a good idea to create an RFC on this, I will need to get some RFC karma - my wiki account is nunomaduro. Regards, Nuno - https://twitter.com/enunomaduro.