You can kind-of do it in C/C++. Unless the function is inlined. The sad reality is that the optimizer screws you over here - either you run your code unoptimized, with all the metadata present (no inlined functions, every function and every method of every class has a symbol, etc.), or you run your program fast. There is no notion of de-optimizing the binary, replacing the definition of a function and then re-optimizing.

You could write that, but it would have to be some kind of hypervisor that combines make+gcc+ld in one package that can dynamically recompile, relink and replace code that changes.