Concepts require understanding.

What this C++20 requires clause question tests

This is an easy practice question on C++20 concept syntax, specifically the requires keyword and how it integrates with template constraints. It assesses whether you understand the distinction between correct and incorrect ways to express compile-time constraints in modern C++.

Candidates working through this problem need to recognise valid requires clause syntax, including where and how constraints can be applied to function templates, and which patterns will actually compile. The question rewards familiarity with the grammar of C++20 concepts rather than deep algorithmic insight.

• Requires clauses on function templates
• Concept definitions vs. constraint expressions
• Placement and scope of constraint predicates