API refactor for rlp.Serializable

[pipermerriam]

I've some thoughts on how we might change rlp.Serializable.

Current features

• immutable vs. mutable objects (make_mutable, make_immutable).
• attribute access to fields
• instantiation with either *args or **kwargs
• cls.exclude API for creating classes with a subset of fields

Inefficiencies

• mutability checks at runtime
• field assignment done exclusively through __setattr__ (60% faster to use direct attribute assignment)
• obj.fields is non-ideal since it disallows the use of any field named fields

Solution

• use collections.namedtuple for immutable versions of the object. Fields are naturally ordered, and immutability is enforced by default.
• use a dynamically constructed class for mutable versions of the object.

[pipermerriam]

@carver and @gsalgado thoughts?

[carver]

Seems reasonable. It would be nice to think through how we would need to re-work current subclasses, like: https://github.com/ethereum/eth-rlp/blob/master/eth_rlp/main.py#L13

[pipermerriam]

It would be nice to think through how we would need to re-work current subclasses

The one major breaking change that I want to make is removal of obj.fields. Otherwise, I don't see anything in the linked example that would need to be reworked. I'm implementing __iter__ for use internally, so you'd even be able to remove that from the subclass.

[wjmelements]

I don't see any make_mutable. The only apparent way to make it mutable is to set _in_mutable_context to True

[carver]

IIRC we settled on an immutable-only approach.