The runtime behavior I was alluding to with C++ would be exceptions, which dramatically changed the language compared to c—I'd peg the demise of C++-as-a-supers

The runtime behavior I was alluding to with C++ would be exceptions, which dramatically changed the language compared to c—I'd peg the demise of C++-as-a-superset-of-C with the death of cfront in 93: https://en.wikipedia.org/wiki/Cfront https://en.wikipedia.org/wiki/Cfront