Class values as CheckedDict type-arguments are not handled properly about cinder

[DinoV]

The difficulty with disallowing a dynamic type is we do want to allow it sometimes. We have things like CheckedDict[str, Set[...]]. In this case other type checkers happily see the Set[...] type and CheckedDict as an alias for Dict and enforce the appropriate types. But we just see Set[...] as dynamic, and turn it into a CheckedDict[str, object].

So I think disallowing it ends up being worse than making it work. I have a fix which would make this work for CheckedDict by getting rid of __new__ so that our allocation will go through TP_ALLOC which takes a type descriptor. Unfortunately if we ever want a generic type which is immutable (which would presumably take arguments) then we'll run into this again.

There's probably a couple of possible solutions for that. One might be to add a way to invoke __new__ that takes the type descriptor and passes the resolved type in as the 1st argument (i.e. a TP_NEW opcode). What might be better would be adding an opcode which turns a type descriptor into the underlying type. Then we could emit the __new__ call with the compiler known type instead of emitting the various loads and binary subscrs required to produce the type. That might not require any specialization of the __new__ handling - we could just use that to emit any generic type references.

[carljm]

There is no dynamic at runtime, dynamic is purely a compiler construct. If a dynamic type ends up in the bytecode, it gets translated to object.

I think probably what we want here is the static type error on trying to make a CheckedDict with dynamic type as key or value type.

[DinoV]

The problem here is that we think we want to create a CheckedDict[str, dynamic] because we don't know what C resolves to. But we then call CheckedDict.__new__(CheckedDict[str, C]) to create the instance of it.

[bennn]

Is chkdict[str, object].__new__ the same as CheckedDict.__new__ (the right constructor)? We were wondering how object got involved, as opposed to C or dynamic.

[DinoV]

This is now fixed, we'll make a CheckedDict which respects what the compiler things the type is instead of the runtime provided type. Per the discussion above there'll be more work in the future though.