Re: [PHP-DEV] [RFC][Proposal] Renamed parameters

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July 24, 2020 13:06 phpmailinglists@gmail.com (Peter Bowyer)
As a general point, Python went through this almost 2 years ago. Their PEP
is worth reading (I didn't see it mentioned before):
https://www.python.org/dev/peps/pep-0570/

Peter

On Fri, 24 Jul 2020 at 12:13, Chris Riley 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 >