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Date: Sun, 26 Jul 2020 14:52:07 +0100
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Subject: Re: [RFC][Proposal] Renamed parameters
From: t.carnage@gmail.com (Chris Riley)

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Hi all,

Thanks for the feedback so far. In light of the feedback received both here
and privately, I've made 3 changes to the RFC document:

1. The original option 1, allowing renaming parameters but not requiring an
explicit opt in to enable them to be called by name has been dropped. The
proposal is now only for explicit opt in parameters with renaming as a
possibility. The reasoning for this, is that although I included option 1
as I thought it might be more likely to be accepted; many people pointed
out that we are very close to the cutoff date for PHP 8.0 and that
implementing such a change would likely be too big to get done in time.
Option 1 would be possible to include in PHP 8.1 as it doesn't break BC,
this means that the proposal can be brought back targeting 8.1 should
option 2 not be accepted.

2. With respect to the feature freeze date, I've added a possible strategy
to deal with a staged implementation, should the release managers not feel
comfortable including the full feature at this late stage.

3. I have documented the main objections to the RFC on the RFC itself and
included my rebuttals; should anyone feel I've not represented their point
fairly let me know and I'll update.

Regards,
Chris

On Fri, 24 Jul 2020 at 12:12, Chris Riley <t.carnage@gmail.com> wrote:

> Hi all,
>
> The named parameters RFC has been accepted, despite significant objections
> from maintainers of larger OSS projects due to the overhead it adds to
> maintaining backwards compatibility as it has now made method/function
> parameter names part of the API; a change to them would cause a BC break
> for any library users who decide to use the new feature.
>
> It is likely that the way this will shake out is that some maintainers
> will accept the additional overhead of including parameter names in their
> BC guidelines and others will not, this leaves users unsure if they can use
> the new feature without storing up issues in potentially minor/security
> releases of the libraries they use. This is not really an ideal situation.
>
> More pressing a point is that the current implementation breaks object
> polymorphism. Consider this example (simplified from one of my codebases)
>
> interface Handler {
>     public function handle($message);
> }
>
> class RegistrationHandler implements Handler {
>     public function handle($registraionCommand);
> }
>
> class ForgottenPasswordHandler implements Handler {
>     public function handle($forgottenPasswordCommand);
> }
>
> class MessageBus {
>     //...
>     public function addHandler(string $message, Handler $handler) { //... }
>     public function getHandler(string $messageType): Handler { //... }
>     public function dispatch($message)
>     {
>         $this->getHandler(get_class($message))->handle(message: $message);
>     }
> }
>
> This code breaks at run time.
>
> Proposals were made for resolutions to this issue however all of them
> require trade offs and could potentially break existing code.
>
> My proposal to resolve these two issues is to add the ability to rename
> parameters with a new syntax as follows.
>
> function callBar(Foo $internalName:externalName) {
>     $internalName->bar();
> }
>
> $x = new Foo();
> callBar(externalName: $x);
>
> This allows both the above problems to be resolved, by renaming the
> internal parameter and keeping the external signature the same.
>
> I propose that the RFC would have two voting options.
>
> The first would be to implement it as proposed above, this would allow any
> parameter to be called by name regardless of the intentions of the author
> of the method/function and is closest to the current behaviour.
>
> The second option would be to use this syntax to make named parameters in
> userland code explicitly opt in. As such an additional shortcut syntax
> would be implemented: $: to designate a named parameter. eg
>
> function callBar($:externalName) {
>     $externalName->bar();
> }
>
> $x = new Foo();
> callBar(externalName: $x);
>
> If a parameter is not opted in, a compile time error is raised:
>
> function callBar($externalName) {
>     $externalName->bar();
> }
>
> $x = new Foo();
> callBar(externalName: $x); // Error: cannot call parameter $externalName
> by name.
>
> There are pros and cons to this second approach, on the one hand it
> reduces the usefulness of the named parameter syntax by requiring changes
> to old code to enable it (although this could probably be automated fairly
> easily) however it does provide a neater solution to the second problem in
> that, to prevent the runtime errors in the second issue example, every
> child class would need to use the rename syntax on it's parameter to
> prevent errors, whereas if we went down this route, the parent class could
> just not opt into the named parameter syntax and the code would function as
> expected.
>
> Another advantage is that with the ability to rename parameters using the
> opt in, we gain some flexibility to tighten up the LSP rules relating to
> named parameter inheritance.
>
> class Foo {
>     public function bar($:param) { //... }
>     public function baz($internal:external) { //... }
> }
>
> // OK
> class Bar {
>     public function bar($renamed:param) { //... }
>     public function baz($renamed:external) { //... }
> }
>
> // Compile time error cannot rename named parameter $:param (renamed to
> $:renamedParam)
> class Baz {
>     public function bar($:renamedParam) { //... }
> }
>
> // Compile time error cannot rename named parameter $:external (renamed to
> $:renamed)
> class Baz {
>     public function baz($internal:renamed) { //... }
> }
>
> While this would be technically possible with the first option (no opt in)
> it would break any existing code which renames a parameter as every
> parameter would be subject to these rules.
>
> I don't have Wiki karma so can't post this yet; but I want to get the ball
> rolling on discussion as feature freeze is coming up fast and if we want to
> go for the second option, that must hit before the named parameter syntax
> is in a tagged version of PHP.
>
> Regards,
> Chris
>

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