Map with bind: match Tuple of parameterized types with parameters from TypeVarTuple

PEP-646 で取り下げられた Map の議論と、参照されている typing issue #193 のコメントから始め、続いて Tuple と TypeVarTuple のパラメータのマッチングに関するリンク先の議論を読んでください。提案されている bind argument を曖昧さなく仕様化できるか、またそれに必要な型チェックの動作を判断してください。合意された仕様、または範囲が明確な実装計画を作成できれば完了です。

Prior work in PEP-646 on Map was dropped to simplify it, with a promise it would appear in a future PEP. Here is a reference to the dropped Map feature: https://github.com/python/typing/issues/193#issuecomment-782689251

Here is an discussion of a potential usage of this Map feature for matching argument types for a length-n Tuple of unary Callables with a length-n Tuple parameterized by a TypeVarTuple: https://groups.google.com/g/dev-python/c/SbPOxIEvI60?pli=1

Here is a draft spec of PEP-646 that included discussion of Map: https://github.com/python/peps/blob/bf897f8c839d1b4d4534ab1fa223a210e2cacf06/pep-0646.rst

I would like to propose an extension of Map with a "bind" argument to allow disambiguation in case the parameterized type has multiple generic parameters. To give an example:

###########
## Converting from multiple domains to a common codomain
############

Domain = TypeVar('Domain')
Codomain = TypeVar('Codomain')

class Detector(Generic(Domain)):
    def __init__(self, detector_fn: Callable[[Any], Optional[Domain]):
        self.detector_fn = detector_fn

    def detect(arg: Any) -> Optional[Domain]
         # returns `arg` if `arg` belongs to Domain, otherwise returns None
        return self.detector_fn(arg)

class Converter(Generic[Domain, Codomain]):
    def __init__(self, converter_fn: Callable[[Domain], Codomain]):
        self.converter_fn = converter_fn

    def convert(arg: Domain) -> Codomain:
        return self.converter_fn(arg)

Domains = TypeVarTuple('Domains')

class ConverterCollection(Generic[*Domains, Codomain]):
    def __init__(self, detectors: Tuple[*Map[Detector, Domains]], converters: Tuple[*Map[Converter, Domains, bind=Domain]]):
        self.detectors = detectors
        self.converters = converters

    def convert(self, obj_to_convert: Union[*Domains]) -> Codomain:
        for detector, converter in zip(self.detectors, self.converters):
            detected_object = detector.detect(obj_to_convert)
            if not (detected_object is None):
                return converter.convert(object_to_convert)
        raise ValueError('No converter for object.')

### Usage

int_detector = Detector[int](lambda x: x if isinstance(x, int) else None)
int_converter = Converter[int, str](lambda x: json.dumps(x))

float_detector = Detector[float](lambda x: x if isinstance(x, float) else None)
float_converter = Converter[float, str](lambda x: json.dumps(x))

cc = ConverterCollection[int, float, str](
    (int_detector, float_detector),
    (int_converter, float_converter)
)

cc.convert(2)    # works
cc.convert(2.0) # also works
cc.convert('hi')  # type error

The bind=Domain argument here would be because Converter class is generic in both Domain and Codomain, so there is ambiguity about which generic parameter to Map. This is not necessary for Detector because, because it is generic only over Domain, so there is no ambiguity what to map over.