The reason a simple set() won't work is that the "thing" put into the container is generally not a value but instructions for how to produce a value on-demand, and the value is typically a service object. How to encode "here's how to build the thing" is the main question to answer.
--Larry Garfield On Friday, March 2, 2018 1:18:32 PM CST David Lundgren wrote: > If the problem to solve is "what's a common way to put things in a > container?" wouldn't the simplest solution be a `set($id, $value)` method > on the container? > > Most container implementations already have a method of this sort. While a > few have shared/concrete/protected concepts baked in, they could make > separate methods for changing it based on the $id. > > Dave > > On Thursday, March 1, 2018 at 11:16:29 AM UTC-6, David Négrier wrote: > > Hey list, > > > > We are still in the process of forming a working group regarding a Service > > provider PSR. > > > > I've had the chance to speak about this with several Symfony contributors, > > and while discussing about this idea, Nicolas Grekas > > <https://github.com/nicolas-grekas/> (from Symfony) came up with an > > alternative proposal. It's about having many containers working together, > > with a slightly different scope. First of all, I'd like to thank Nicolas > > for the time he is investing in researching this issue, and for all the > > feedback. We talked about his idea with Matthieu Napoli > > <https://github.com/mnapoli/> and Larry Garfield > > <https://github.com/crell> at the Paris ForumPHP in November. I'm now > > sharing this conversation with you. > > > > I put this in a blog article that you can find here: > > https://thecodingmachine.io/psr-11-scope-of-universal-service-providers > > > > I'm reposting the content of the article here, since it's directly related > > to PHP-FIG concerns. It's a bit long, but the topic is worth it :) > > > > Stated goal > > > > Each framework has it's own custom package format (bundles, packages, > > modules, etc...). What these package formats are doing is essentially > > always the same. They are used to put things in a container. > > > > If the PHP-FIG could come up with a unique package format that could be > > supported by all frameworks, package developers could truly write classes > > that can be used in any framework more easily. > > > > Hence, the stated goal of this PSR (let's call it PSR-X since it does not > > have a number yet) is to find a common way to *put things in a container*. > > > > We (the container-interop group) have been working on this for quite some > > time and have come up with a solution that needs to be turned into a PSR > > <https://github.com/container-interop/service-provider/>. The idea is to > > build generic service providers. > > > > > > Current proposal > > > > The current proposal is named container-interop/service-provider > > <https://github.com/container-interop/service-provider/>. In this > > proposal, we create a ServiceProviderInterface interface that exposes a > > set of *factories*. > > > > > > class MyServiceProvider implements ServiceProviderInterface{ > > > > public function getFactories() > > { > > > > return [ > > > > 'my_service' => function(ContainerInterface $container) : > > MyService { > > > > $dependency = $container->get('my_other_service'); > > return new MyService($dependency); > > > > } > > > > ]; > > > > } > > > > // ... > > > > } > > > > > > In the example above, the 'my_service' service can be created by the > > container by executing the factory (the anonymous function). > > > > Additionally, the ServiceProviderInterface let's you *modify* existing > > services stored in the container. > > > > > > class MyServiceProvider implements ServiceProviderInterface{ > > > > // ... > > > > public function getExtensions() > > { > > > > return [ > > > > Twig_Environment::class => function(ContainerInterface > > $container, Twig_Environment $twig) : Twig_Environment {> > > > > $twig->addExtension($container->get('my_extension')); > > return $twig; > > > > } > > > > ]; > > > > } > > > > } > > > > > > In the example above, the service named "Twig_Environment" is modified. We > > register a new twig extension in it. This is very powerful. This can be > > used to create arrays and add elements to them, or this can be used to > > decorate an existing service (using the decorator pattern). Overall, this > > gives a lot of power to the service provider. > > > > Right now, this interface has been tested. It has adapters in Symfony, > > Laravel, and there is a Pimple fork named Simplex that is also > > implementing > > it. You can view the complete list of implementations here > > <https://github.com/container-interop/service-provider#compatible-projects > > > > > . > > > > > > The alternative proposal > > > > Nicolas Grekas and the Symfony team came up with another proposal > > <https://github.com/symfony/symfony/pull/25707>. > > > > Rather than standardizing service providers, he proposes that each package > > could provide it's own container. The container would have an interface to > > expose a list of services to your application's container. > > > > The proposal goes like this: > > > > > > interface ServiceProviderInterface extends ContainerInterface{ > > > > /** > > > > * Returns an associative array of service types keyed by names > > provided by this object. * > > * Examples: > > * > > * * array('logger' => 'Psr\Log\LoggerInterface') means the object > > provides service implementing Psr\Log\LoggerInterface * under > > "logger" name > > * * array('foo' => '?') means that object provides service of > > unknown type under 'foo' name * * array('bar' => '?Bar\Baz') means > > that object provides service implementing Bar\Baz or null under > > 'bar' name * > > * @return string[] The provided service types, keyed by service names > > */ > > > > public function getProvidedServices(): array; > > > > } > > > > > > Notice how the ServiceProviderInterface extends the PSR-11 > > ContainerInterface <https://www.php-fig.org/psr/psr-11/>. > > > > Here, there is a single function getProvidedServices that provides the > > names of the provided services as keys, along the type of the service as > > values. > > > > When your application's container is asked for a service that is part of a > > "service provider", it would simply call the get method of the service > > provider (since a service provider IS a container) and retrieve the > > service. > > > > There is no way for a service provider to modify services in the > > application's container (this is a design decision). > > > > While talking about this interface, we also mentioned another interface. A > > service provider can need dependencies stored in another container. It > > could therefore publish the list of services it is expecting to find in > > the > > main container. Therefore, Nicolas proposed an additional interface: > > ServiceSubscriberInterface, providing a getSubscribedServices method. > > > > > > class TwigContainer implement ServiceProviderInterface, > > ContainerInterface, ServiceSubscriberInterface {> > > //... > > > > public function getSubscribedServices() > > { > > > > // The TwigContainer needs 2 services to be defined: > > // - "debug" (this is an optionnal bool value) > > // - "twig_extensions" (this is an optionnal array of objects > > implementing TwigExtentionInterface) return [ > > > > 'debug' => '?bool', > > 'twig_extensions' => '?'.TwigExtentionInterface::class.'[]', > > > > ]; > > > > } > > > > } > > > > > > Notice that the 2 interfaces can be considered independently. The > > ServiceSubscriberInterface allows to add an additional check at container > > build time (vs getting a runtime exception if a service is lacking a > > container entry or if the provided container entry is of the wrong type). > > > > > > Comparing of the 2 proposalsRegarding performance > > > > Regarding performance, the 2 proposals have very different properties. > > > > > > *In container-interop/service-providers*: > > > > The service provider is largely considered as *dumb*. It is *the > > responsibility of the container* to optimize the calls. > > > > Actually, it is possible to get excellent performances if the service > > provider is providing the factories as public static functions. > > > > class MyServiceProvider implements ServiceProviderInterface{ > > > > public function getFactories() > > { > > > > return [ > > > > Twig_Environment::class => [ self::class, 'createTwig' ] > > > > ]; > > > > } > > > > public static function createTwig(ContainerInterface $container, > > Twig_Environment $twig) : Twig_Environment {> > > $twig->addExtension($container->get('my_extension')); > > return $twig; > > > > } > > > > // ... > > > > } > > > > In this case, a compiled container could directly call the factory, > > without having to instantiate the service provider class nor call the > > getFactories method. This is definitely the best performance you can get > > (but is still to the good-will of the service-provider author that must > > use public static methods instead of closures). > > > > > > *In Symfony's proposal*: > > > > The service provider is an actual container. *The service provider is > > therefore in charge of the performance of delivered services*. > > > > It probably cannot beat the direct call to a public static function > > (since you have to call at least the service provider constructor and the > > get function of the service provider), but can still be quite optimized. > > The important part is that the performance is delegated to the service > > provider. > > > > Dealing with service names > > > > *In container-interop/service-providers*: > > > > The idea is that service providers should respect some kind of convention. > > > > If you are writing a service provider for Monolog, the service creating > > the Monolog\Logger class should be named Monolog\Logger. This will allow > > containers using *auto-wiring* to automatically find the service. > > > > Additionally, you can create an *alias* for your service on the > > Psr\Log\LoggerInterface, if you want to auto-wire the LoggerInterface to > > the Monolog\Logger service. > > > > The code would therefore look like this: > > > > > > class MonologServiceProvider implements ServiceProviderInterface{ > > > > public function getFactories() > > { > > > > return [ > > > > \Psr\Log\LoggerInterface::class => [ self::class, > > 'createAlias' ], > > \Monolog\Logger::class => [ self::class, 'createLogger' ], > > > > ]; > > > > } > > > > public static function createLogger(): \Monolog\Logger > > { > > > > return new \Monolog\Logger('default'); > > > > } > > > > public static function createAlias(ContainerInterface $container): > > \Monolog\Logger { > > > > return $container->get('\Monolog\Logger'); > > > > } > > > > // ... > > > > } > > > > > > *In Symfony's proposal*: > > > > I must admit I'm not 100% clear on Nicolas thought here. There are really > > 2 solutions. Either we adopt a convention (just like with > > container-interop/service-provider), either we can decide that the > > container can be "clever". After all, using the getProvidedServices > > class, a container can know the type of all provided services, so if it > > could decide to autowire them by its own. > > > > For instance, if a call to getProvidedServices returns: > > > > [ > > > > 'logger' => '\Monolog\Logger' > > > > ] > > > > the container could decide on its own that the 'logger' service is a good > > fit to auto-wire '\Monolog\Logger'. > > > > At this stage, the decision is delegated to the container. The service > > provider is more "dumb". It does not know and does not decide what gets > > auto-wired. The container does (this means there is probably some > > configuration required in the container). > > > > Dealing with list of services > > > > It is pretty common to want to add a service to a list of services. In > > containers, this is usually done by using "tags". None of the 2 proposals > > supports the notion of tags directly. But both have workarounds. > > > > > > *In container-interop/service-providers*: > > > > The idea is to create an entry in the container that is actually an array > > of services. Each service provider can then modify the array to register > > its own service in it. > > > > class MonologHandlerServiceProvider implements ServiceProviderInterface{ > > > > // ... > > > > public function getExtensions() > > { > > > > return [ > > > > HandlerInterface::class.'[]' => function(ContainerInterface > > $container, array $handlers = []) : array {> > > $handlers[] = new MyMonologHandler(); > > return $handlers; > > > > } > > > > ]; > > > > } > > > > } > > > > > > *In Symfony's proposal*: > > > > The PR does not state it, but we could imagine allowing types with '[]' at > > the end. > > > > For instance, if a call to getProvidedServices returns: > > > > [ > > > > 'monologHandlers' => HandlerInterface::class.'[]' > > > > ] > > > > then the container might decide to automatically append the services > > returned by 'monologHandlers' to services with the same name in the main > > container. > > > > Said otherwise, the container calls get('monologHandlers') on all the > > service providers and concatenates those. > > > > Dealing with list of services with priorities > > > > Sometimes, you are adding a service in a list that must be ordered. > > > > Let's take an example. You just wrote a PSR-15 middleware that is an error > > handler (like the Whoops middleware > > <https://github.com/middlewares/whoops>). This middleware must absolutely > > be the first to be executed in the list of middlewares (because it will > > catch any exception that might be thrown by other middlewares). > > > > Some containers allow to tag with priorities. But we don't have this > > notion in our interfaces. > > > > How can we deal with that? > > Do we need this? Discussing with Matthieu Napoli, I know that Matthieu > > thinks this can be out of scope of the PSR. In Matthieu's view, it is not > > the responsibility of the service provider to decide where a service is > > inserted in a list. I personnally feel this is quite an important feature. > > An error handling middleware knows it must be at the very beginning so I > > think we (the service providers authors) should do all what we can to help > > the developer using our middleware to put it at the right spot. For the > > author of the Whoops middleware service provider, it is quite obvious that > > the middleware must go first. For the average PHP developer that is not an > > expert in middleware architectures, it might be far less obvious. > > > > > > *In container-interop/service-providers*: > > > > The idea is to create an entry in the container that is a priority queue. > > For instance, PHP has the great \SplPriorityQueue. > > > > class WhoopsMiddlewareServiceProvider implements ServiceProviderInterface{ > > > > // ... > > > > public function getExtensions() > > { > > > > return [ > > > > 'middlewareList' => function(ContainerInterface $container, > > \SplPriorityQueue $middlewares) : \SplPriorityQueue {> > > > > $middlewares->insert(new WhoopsMiddleware(), -9999); > > // Note: we should replace the -9999 by a constant like > > MiddlewarePriorities::VERY_EARLY return $middlewares; > > > > } > > > > ]; > > > > } > > > > } > > > > > > *In Symfony's proposal*: > > > > How to deal with this in Symfony's proposal is quite unclear to me. > > > > We could decide this is out of scope. > > > > We could also decide that we have many unsorted list, like > > 'earlyMiddlewares', 'utilityMiddlewares', 'routerMiddlewares'... that are > > concatenated by the middleware service provider and fed to the middleware > > pipe. > > > > Miscellaneous 1: introspection > > > > Symfony's proposal has 2 wonderful features that > > container-interop/service-provider does not have. They are not directly > > > > necessary to our stated goal, but are quite nice: > > - the ServiceProviderInterface is actually an introspection interface > > into any container implementing it. This gives us a lot of room to > > write > > cross-framework tools that can scan containers and analyze them. Pretty > > cool. > > - the fact that a service provider can publish the list of > > dependencies it needs (the ServiceSubscriberInterface) is in my > > opinion a very good idea. A service provider offers some entries but > > can > > > > also require some entries. By publishing its requirements, we get: > > - automated documentation > > - the possibility to do static analysis > > - the possibility to write tool chains that help the developer set > > up service providers (think about a huge online database of all > > service > > providers available on Packagist with what they offer and what they > > require > > > > :) ) > > > > Miscellaneous 2: factory services > > > > PSR-11 recommends that 2 successive calls to get should return the same > > entry: > > > > Two successive calls to get with the same identifier SHOULD return the > > same value. > > > > Indeed, a container contains services. It should not act as a factory. > > Yet, it does not forbid containers to act as a factory (we used "SHOULD" > > and not "MUST" in PSR-11). *container-interop/service-provider* on the > > other end is very explicit. The service provider provides factories, and > > the container MUST cache the provided service. So for services provided by > > *container-interop/service-provider*, 2 successive calls to the container > > MUST return the same object. I don't see this as a problem, rather as a > > feature. Yet, with Symfony's proposal, since calls to "get" are delegated > > to the service provider (that is a container itself), we could write a > > service provider that provides a new service on each call to get. > > Symfony's > > proposal is more flexible in that regard. > > > > Summary / TL;DR > > > > That table below summarizes the differences between the 2 proposals: > > > > > > > > *container-interop* *Symfony* > > Performance Container is in charge Service provider is in charge > > Service names By convention Can be deduced from types > > Static analysis No Possible > > Modifying services Yes (powerful service providers) No (dumb service > > providers) > > Tagged services Yes, via modified arrays Yes > > Tagged services with priorities Yes, via modified SplPriorityQueues No > > (out of scope?) > > > > > > My thoughts > > This section highlights my current opinions. Others might completely > > disagree and I think it is important we have a discussion about what we > > want to achieve. > > > > By standardizing service providers, we are shifting the responsibility of > > writing the "glue code" from the framework developer to the package > > developer. For instance, if you consider Doctrine ORM, it is likely that > > the Doctrine service provider would be written by the Doctrine authors > > (rather than the Symfony/Zend developers). It is therefore in my opinion > > important to empower the package developer with an interface that gives > > him/her some control over what gets stored in the container. > > > > > > Existing packaging systems (like Symfony bundles or Laravel service > > providers) have already this capability and I believe we should aim for > > this in the PSR. > > > > > > Taking the "PSR-15 Whoops middleware" example, it is for me very important > > that the service provider author can decide where in the middleware pipe > > the middleware is added. This means being able to add a service at a given > > position in a list (or having tags with priorities). This, in my opinion, > > should be in the scope of the PSR. > > > > Said otherwise, while registering the service provider in the container, > > the user should be able to write: > > > > > > $container->register(new WhoopsMiddlewareServiceProvider()); > > > > > > instead of something like: > > > > > > $container->register(new WhoopsMiddlewareServiceProvider(), [ > > > > 'priority' => [ > > > > WhoopsMiddleware::class => -999 > > > > ] > > > > ]); > > > > > > In this regard, I feel the *container-interop/service-provider* proposal > > is better suited (because it allows to modify an existing service and that > > is all we need). > > > > That being said, the proposal of Nicolas has plenty of advantages I can > > > > also very well see: > > - container introspection > > - better maintainability/documentation through better tooling > > > > I have a gut feeling that there is something that can be done to merge the > > 2 proposals and get the best of both worlds. Or maybe we can have the 2 > > proposals live side by side (one for service providers and the other for > > container introspection?) > > > > > > What do you think? > > > > What should be the scope of the PSR? > > > > For you, is it important to give service provider some control over the > > container or should they be "dumb" and just provide instances (with the > > controller keeping the control on how the instances are managed)? > > > > > > ++ > > > > David > > > > Twitter: @david_negrier > > > > Github: @moufmouf -- You received this message because you are subscribed to the Google Groups "PHP Framework Interoperability Group" group. To unsubscribe from this group and stop receiving emails from it, send an email to php-fig+unsubscr...@googlegroups.com. To post to this group, send email to php-fig@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/php-fig/6818461.mtiu81ZDCD%40vulcan. 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