Concepts (C++20)

Concepts let you express template requirements directly in code, which improves diagnostics and documents intent.

Built-in Concepts

#include <concepts>

template <std::integral T>
T add_one(T v) {
  return v + 1;
}

Custom Concepts

template <typename T>
concept Addable = requires(T a, T b) {
  { a + b } -> std::same_as<T>;
};

template <Addable T>
T add(T a, T b) {
  return a + b;
}

Where Concepts Help Most

• Template-heavy codebases
• Public generic APIs
• Constraining algorithm input types

[!NOTE] Concepts reduce cryptic template error messages by failing at the constraint boundary.