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Date: Fri, 24 Jul 2020 14:15:17 +0100
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To: Benjamin Eberlei <kontakt@beberlei.de>
Cc: PHP internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary="0000000000004309c705ab2fc4f9"
Subject: Re: [PHP-DEV] [RFC][Proposal] Renamed parameters
From: t.carnage@gmail.com (Chris Riley)

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On Fri, 24 Jul 2020 at 14:01, Benjamin Eberlei <kontakt@beberlei.de> wrote:

>
>
> On Fri, Jul 24, 2020 at 1:13 PM 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.
>>
>
> Hi Chris,
>
> I had something similar in mind, but using an attribute. Here is a patch
> that already allows this:
>
>
> https://github.com/beberlei/php-src/commit/4b0a02f9c6ba579f93ec57c754fa3794a96c696b
>
> Idea: Have a @@NameAlias attribute, where you can provide a second name
> for the attribute. This would allow to refactor parameter names by adding
> the attribute with the old name as an alias.
>
>
>>
>> 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
>>
>
Hi,

While the attribute idea does solve the BC problems, I'm not seeing how it
really solves the polymorphism issue - could you provide an example of how
this would work?

In either case; as a personal preference I'd rather stick to syntax that
affects the parameter as part of it's definition instead of tweaking it's
behaviour with an attribute. It just feels easier to grasp what is going on.

Regards,
Chris

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