Not given C and C++ separate file compilation.

That might be OK in an IDE driven language such as Java, but I doubt the neckbeards writing C in a plain text editor would go for that level of implicitness. In C++ it might be more acceptable since you practically need an IDE since C++11 to resolve all the auto type inference.

C neckbeard here. I do fully hope and expect and assume the compiler to fold constants and figure out as much at compile time as it can. This is the kind of optimization that doesn't make the code harder to reason about, even when coding with ed, since the logic and ultimate result of these expressions does not change.

Heavy type inference, overloading, and inheritance are a completely different beast and they make the code a lot more opaque.