`T` there would be a trait though, not a type. You should still be able to have, for example, `fn foo<%T>(v: Vec<T>)` in which case you can still call the funct

`T` there would be a trait though, not a type. You should still be able to have, for example, `fn foo<%T>(v: Vec<T>)` in which case you can still call the function with a regular `Vec<i32>`, since if the size/alignment is simply passed as an argument at runtime, you can operate on the existing non-boxed representations of data. The only thing that's different is the specialisation of the instructions essentially happens at runtime rather than at compile time. I have however thought that it should be automatically done based on heuristics, but since the notion of "zero-cost abstraction" is considered the default, I don't think this would be desirable.