Bring them in, boys!

Using variadic templates to combine comparers in C++

This is a medium-difficulty C++ question that tests your understanding of variadic templates and how they interact with standard-library containers. It reflects real code-review scenarios where engineers consolidate boilerplate logic into reusable template abstractions.

The question asks you to refactor two separate functor implementations—a comparator and a hasher for a Customer object stored in a set—into a single variadic template. This requires understanding how to unpack parameter packs, how template specialization works, and which overload patterns allow a single template definition to behave correctly in different contexts (comparison vs. hashing). The prompt tests both your grasp of modern C++ idioms and your ability to reason about template instantiation and function signatures.

• Parameter pack expansion and perfect forwarding
• Operator overloading in functor templates
• Specialization and SFINAE constraints
• Standard-library container requirements (comparator and hash function signatures)