I recently ended up creating translation unit-static functions for more strict access patterns with stdx::unordered_map/_set. I suspect that a set of helpers with invariants might be more useful to the codebase at large:

• getOrInvariant() which invariants that the key already exists (roughly equivalent to at()).
• emplaceOrInvariant() which invariants that the key did not already exist.
• eraseOrInvariant() which invariants that the key existed and will no longer.

This set of operations allows a developer to confidently use a map or set to contain a unique set of initialized objects.