Constraint Subsumption in Action

What this C++ template constraint question tests

This is a medium-difficulty C++ question that probes your understanding of how the compiler resolves function overloads when multiple template specializations are available. It rewards careful reading of template constraints and the rules governing which candidate is selected.

To solve problems like this, you need to trace through the constraint-satisfaction logic and understand how subsumption — the principle that a more specific constraint defeats a more general one — determines which overload the compiler will choose. The question tests whether you can reason precisely about template instantiation and overload resolution, skills that matter in modern C++ codebases and in high-performance contexts where template metaprogramming is common.

• Template specialization and partial ordering
• Constraint satisfaction and subsumption rules
• Function overload resolution with concepts (C++20)