Provide method to fetch FlashMessages from Request about mezzio-flash

[weierophinney]

Why did you event allow setting a custom attribute key?

To allow usage of multiple different FlashMessageMiddleware instances that were capable of segregating their own sets of messages, without having to worry about naming collisions. When such a scenario is in play, you either hard-code in the other middleware and handlers the other attribute value, or, better, inject it as a dependency.

We tend to discourage static methods within the framework, as they lead to tight coupling, and discourage the ability to have multiple configurations — which is exactly what the configurable attribute key is for.

One possible alternative would be to provide an instance method on the FlashMessageMiddleware, and then compose the middleware as a dependency on anything that needs to fetch messages:

public function __construct(FlashMessageMiddleware $flashContainer)
{
    $this->flashContainer = $flashContainer;
}

public function handle(ServerRequestInterface $request): ResponseInterface
{
    $messages = $this->flashContainer->flashMessages($request);
    // ...
}

That said, the following would be similar, and can be done now:

public function __construct(string $flashAttribute)
{
    $this->flashAttribute = $flashAttribute;
}

public function handle(ServerRequestInterface $request): ResponseInterface
{
    $messages = $request->getAttribute($this->flashAttribute) ?? [];
    // ...
}

To sum up:

• Having a configurable attribute name was a design decision to allow segregating messages by domain.
• As a general rule, we do not provide static methods within the framework, and have, in fact, worked to remove them where we previously had them.
• Any helper method would have to be attribute-aware, and provide significant convenience over what is already possible.

[rieschl]

Thanks for the detailed explanation! Yes, the configurable attribute key somewhat defeats the usage of such a static method. And of course, coupling in the framework is an issue, Inside my own projects the coupling is less of a problem, so I did not think of that.
But it's okay, I just stick with my own helper method in the project.