The Regular Type Hierarchy

Understanding C++ standard concept refinement hierarchy

This medium-difficulty C++ question tests your grasp of the standard library's concept hierarchy introduced in C++20. It rewards familiarity with how std::movable, std::copyable, std::semiregular, and std::regular relate to one another — and specifically, which concepts are more general and which impose stricter constraints.

Questions like this appear in coding rounds at firms that work heavily with modern C++ templates and generic programming. The hierarchy matters because it governs which types satisfy which concepts, and therefore which template instantiations are valid. Understanding the ordering helps you reason about type constraints, API design, and whether a given type can be safely used in a particular context.

• Concept subsumption and refinement
• Move semantics vs. copy semantics
• Equality comparison as a semantic requirement
• Default-constructibility and its role in regularity