Protocols and dataclass-based components

glyph.py

"""

https://github.com/python/mypy/issues/4717#issuecomment-454609539

Hi Glyph, thanks for reading. This is going to take a while.

I'm interested in pluggable systems. Specifically a better Sphinx rendering
layer, which I've spent a lot of time on. Recently I've worked on Michael
Merickel's wired:
https://wired.readthedocs.io/
Specifically I wrote the dataclass-based injector, which uses dataclass
field metadata to give instructions to the injector.

wired makes it easy to register multiple implementations for a class or
interface. But classes kind of suck, because the "interface" is an
implementation (class). However interfaces still have poor tooling
support, even with mypy-zope.

(I won't belabor the point about wired, DI, and the React-style component
stuff I'm working on. Not necessary to this.)

I'm interested in PEP 544 protocols because they have a chance to be more
adopted than interfaces. In the example


"""
from dataclasses import dataclass
# This starts the part that is in framework space, so civilians don't
# have to see it, their tooling, e.g. IDE autocomplete, just starts
# working.
from typing import Callable, Type, TypeVar

from typing_extensions import Protocol

protocol = TypeVar("protocol")


# In wired, this decorator also handles a registration in the registry,
# as well as a constructor which sniffs the dataclass fields to do the
# DI.
def component(c: Callable[[], protocol]) -> Callable[[Type[protocol]], Type[protocol]]:
    def decor(input_value: Type[protocol]) -> Type[protocol]:
        return input_value

    return decor


# /end framework space

# This is done by the creator of some sexy library of ready-to-go
# components. The average consumer doesn't see this.
class Heading(Protocol):
    x: int


@component(Heading)
@dataclass
class GoodHeading:
    x: int
    other: str


@component(Heading)
@dataclass
class BadHeading:
    y: int


# /end component library author consumer

# I will leave out what the end-user will see, as it is specific to
# the work I'm doing.

if __name__ == '__main__':
    good = GoodHeading(x=3, other='xyz')
    bad = BadHeading(y=3)