Spot the Invalid Syntax

What this C++ template syntax question tests

This is an easy multiple-choice question on C++ template metaprogramming and type constraints. It checks whether you can distinguish between valid and invalid syntax for restricting template instantiation to specific type categories—in this case, floating-point types.

The question rewards familiarity with modern C++ tools for type checking: std::enable_if, std::is_floating_point, concepts (C++20), and SFINAE principles. Even at quant firms with older codebases, understanding the semantic differences between these approaches helps you write clearer, more maintainable generic code and catch subtle bugs during code review.

• SFINAE and template specialization
• Type traits and the <type_traits> library
• C++20 concepts as a modern alternative
• Common pitfalls in template constraint syntax