Thank you @dunglas.

By the way, do not serialising \Traversable objects forces us to create a custom normalizer for every domain object that is a collection...

As it'd be a really convenient feature, what do you think about adding an optional \Traversable normalizer that would be enabled only explicitly like that ?

framework:
    serializer:
        normalizers: 
            traversable: true

Well, that can be a way of doing for all normalizers by the way.

/cc @dunglas & @fabpot

The flag can be passed to the constructor of normalizers an the supports method can use it.

I would prefer a dedicated normalizer that just delegates normalization of each item to other normalizers (though the chained one) instead of putting more conditions in existing normalizers.

I agree. What about the reverse side of #14343 ?

Yeah, it'd be nice. Maybe this PR should also supports deserialization of any \Traversable but introducing an interface that defines a static constructor, which that a given traversable would implement.

I've some other ideas like the ability to define an accessor for given attributes, so... is the serializer features are frozen because of 2.7 beta or is it still open ?

It's frozen for 2.7 but open for 2.8 and 3.0.

To be more precise, it's frozen for 2.7, open for 2.8, closed for 3.0. All new features must happen in 2.8, not 3.0.