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
>

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