Preparation for immutable objects

[shadowhand]

Right now it is not possible to modify an immutable object using prepare. For instance, I might want to do this (as a contrived example):

$injector->prepare('Zend\Diactoros\Response', function (&$response) {
    $response = $response->withHeader('X-API-Version', 'v2.1');
});

Attempting this will currently produce the following error:

Warning: Parameter 1 to {closure}() expected to be a reference, value given

Because reflection is used to execute the closure, it is not possible to use references.

What is the best way to handle immutable preparation?

[J7mbo]

Hmm, looks like you're trying to tell the injector to, when it encounters an instance of Zend\Diactoros\Response, inject an altered version of it (with the header). Have you considered instantation delegation for this (basically, a factory).

This way your implementation doesn't know about the injector.

$apiResponseFactory = function() use ($response) {
    return $response->withHeader('X-API-Version', 'v2.1');
};

$injector->delegate('Zend\Diactoros\Response', $apiResponseFactory);

Just a suggestion. This might not work for you as it'll need to be in the same context as where you get the $response object.

An alternative would be to grab the injector in the $apiResponseFactory and use that to change the already shared $response. Or maybe that's complete rubbish! Perhaps @rdlowrey can chime in here :-)

[rdlowrey]

This is a sane use-case. There are a couple of options to "fix" prepare() so that this works ... I think the easiest is just to have it check the return value of the prepare callable with an instanceof and if it matches the expected class/interface type have the Injector internally replace the old instance with the newly returned instance.

This would be safe for BC as the return value from prepares wasn't previously meaningful. Can anyone think of any drawbacks to that approach that I may be missing?

Using a delegate like @J7mbo suggested would work, but I try to avoid being forced to instantiate closures when possible in favor of string class method constructions just to make sure things load as lazily as possible (the closure may not always be needed for the particular application resource being loaded).

This would change the OP code to:

$injector->prepare('Zend\Diactoros\Response', function ($response) {
    return $response->withHeader('X-API-Version', 'v2.1');
});

[shadowhand]

@rdlowrey I like that solution very much. Using delegate is not ideal because it forces me to handle the creation of the object or already have it created, which might have unintended consequences if the class is aliased somehow.

[rdlowrey]

Okay, great. I'll try to implement/test/tag that change today. Will post updates here as they happen.

[J7mbo]

The prepare() method change looks much better, I really like that 👍

[rdlowrey]

I've pushed the mentioned change up to master. @shadowhand if you can confirm that works as you expect (you can probably just verify by looking at the new test cases) I will go ahead and tag 1.1.0

[rdlowrey]

This capability is available as of 1.1.0

[kelunik]

👍