• cattrs version: 23.2.3
• Python version: 3.11
• Operating System: Linux

Description

I am bringing in an immutable mapping data type (i.e. immutables.Map https://github.com/MagicStack/immutables) into my code.

I think given that issubclass(immutables.Map, Mapping == True the is_mapping predicate should work for it and there is really no special constructor for it.

What I Did

My first attempt was to register these hooks:

from immutables import Map as frozenmap
...
converter.register_structure_hook(frozenmap, lambda d, t: frozenmap(d))
converter.register_unstructure_hook(frozenmap, lambda d: dict(d))

Which works for a plain frozenmap annotation, but not for generic type specifiers. I can write the hook factory/predicate, but I don't see why the is_mapping code should be specific to mutable mappings: