Last week, I promised a dive into Rust procedural macros as I work to design a DSL for my Widget UI building-block trait. What I've learned is not...
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I usually see PhatomData used with raw pointers like in the nomicon link, but I guess it could hold the type like that.
Text isn't actually using the type, so couldn't it just not be parameterized?:
Maybe I didn't read everything else closely enough.
Yeah, that's what's giving me pause - this use case bears little to no resemblance to the example uses given.
I can't just assign it to some random type, even though I don't use it, because in order to include it in a parent widget it must use the same
MSGtype as every other widget in the tree. The toplevel struct,WindowEngine, demands a member field of typeBox<dyn Widget<MSG = T>>, and theMountedWidget<T>struct also gets parameterized with this type. The compiler complains when I attempt to add a childWidget<MSG = String>to a parent of typeMountedWidget<FiveDiceMessage>, as it should. All the types need to match, even though this particular child will never produce an actual value containing that type.Ah, I see
It's posible it all just means I need to refactor. Ideally I'd like to create a separate
Clickabletrait, but I'm not sure how to check for a trait at runtime. I'd like all of the children to beWidgets but only some to beClickable, and somehow be able to traverse the tree and use either where appropriate, but haven't figured out what that looks like. Is there a way to "detect" another trait implementation after a trait object has been created? My gut says no, that contradicts what I know about trait objects.Just realized I've yet looked at how to do that. Seems std::any::Any is the current solution.
But you're right, I suspect there's more Rust-y way to implement things.
Yeah, I came across that too and played with it a little, but never found anything that didn't feel similarly kludgy. I don't really want to forfeit type checking, seems like a deeper structural change is likely in order.