C++ const is a key feature.
Few people realise that one of the strengths of C++ is that it has had immutable objects from very early days. Many of us have been writing robust OOP systems in C++ enabled by its “const” features. Failing to add this to Java and C# was a fundamental mistake. In the .Net world, F# adds this back at compile level, on top of the mutable CLR, like Clojure adds it back to the JVM.