It isn't like a hypothetical C++ REPL would use unmodified LLM under the hood after all.

It has the limitations mentioned, which are necessary to make duck-typed interface calls reasonably efficient, if you assume no code generation at runtime, ever.

There's really no other way. If you don't know before hand all the interfaces that might exist, and/or all the types that might implement them, interface method calls would necessarily either need to be JIT generated, or a string based hash map lookup (runtime reflection, which exists, but is slow).

Go avoids both by knowing statically at compile time the list of all interface and the list of all types that can ever possibly implement them and building vtables for those.