Concepts (C++20)

1
2
3
4
5
6
7

#include <concepts>

template <std::integral T>
T gcd(T a, T b) { while (b) { T t = b; b = a % b; a = t; } return a; }

gcd(12, 18);    // ok
// gcd(1.5, 2.0);  // error: does not satisfy std::integral

1
2
3
4
5
6
7

template <typename T>
concept Drawable = requires(const T& t, Canvas& c) {
    { t.draw(c) } -> std::same_as<void>;
    { t.bounds() } -> std::convertible_to<Rect>;
};

template <Drawable T> void render(const T& shape);

1
2
3
4
5

template <typename T>
    requires std::copyable<T> && (sizeof(T) <= 64)
void store(T value);

void f(const auto& x) requires Drawable<decltype(x)>;