The inherent overhead of type-erasure is the vtable. Which is funny, because you said you prefer one over the other at the end, when they are basically synonymous. The compiler
may choose to devirtualize and specialize, but that isn't guaranteed. If you want this behavior, &dyn does the exact same thing.
Specialization provides more opportunities for optimizations, whereas proper type-erasure (which bars specialization optimizations) doesn't due to lack of type information.
"C macros" are a part of the preprocessor, which runs before the actual C compiler. As such, it lacks all semantical information the C compiler would have at that point, such as function implementions. In practice, macros in C serve two purposes: manipulating C source code (which Rust macros can also do, but with more hygiene); specialization polymorphism, but worse (in which both Rust's generics and C++ templates do better).
