constexpr Virtual Functions

#include <iostream>
#include <memory>
// Base class with constexpr virtual
struct Shape {
    constexpr virtual ~Shape() = default;
    constexpr virtual double area() const = 0;
    constexpr virtual const char* name() const = 0;
};
struct Circle : Shape {
    double radius;
    
    constexpr Circle(double r) : radius(r) {}
    constexpr double area() const override {
        return 3.14159 * radius * radius;
    }
    constexpr const char* name() const override {
        return "Circle";
    }
};
struct Square : Shape {
    double side;
    
    constexpr Square(double s) : side(s) {}
    constexpr double area() const override {
        return side * side;
    }
    constexpr const char* name() const override {
        return "Square";
    }
};
// Compile-time polymorphism
constexpr double total_area(const Shape& s1, const Shape& s2) {
    return s1.area() + s2.area();
}
int main() {
    constexpr Circle c{5.0};
    constexpr Square s{4.0};
    
    constexpr double total = total_area(c, s);
    static_assert(total > 90.0 && total < 100.0);
    
    std::cout << c.name() << " area: " << c.area() << std::endl;
    std::cout << s.name() << " area: " << s.area() << std::endl;
    std::cout << "Total: " << total << std::endl;
    
    return 0;
}