Or if you (or something you call) mutate it trough another reference/pointer. Sometimes I wish there was a stronger const where the compiler (and programmer) could actually assume the object is not mutated while that reference/pointer is alive. Of course checking that is no longer doable with just the type system.

> You can't even easily copy your way out.

That depends on the type. std::unordered_maps could provide a copy constructor that does the conversion.

And you can do the copy via iterators, although that is probably not as efficient as it could be because it needs to re-hash the keys.

  std::unordered_map<std::string, std::string> m2(m.begin(), m.end());