The source code is parsed to an AST, which is then executed. It began with a Java-Applet. When WebAssembly appeared, I ported it to C++ with a JS/HTML interface and added graphics. Recently I converted the C++ part to C, which halved the size of the wasm file.
One example that is quite amazing in my opinion is Pyret, I think you might like it, check it out at https://www.pyret.org
So you are saying that "costless" abstractions of C++ actually had some cost? Who would have thought.
Size obviously doesn't count. Obviously abstractions will produce more code.
For server/desktop delivery, which is C++ original and major domain, for which those "costless abstractions" were developed, no.
It's not like Stroustrup, Stepanov and co had web assembly and constrained mobile devices loading webpages in mind when designing C++.
The idea of "costless abstractions" was about them not losing runtime speed -- not costless in code size. So the parent's comment doesn't really apply.