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The All-in-One Guide to C++20

Solution: Extend MyInt Class

Understand how to define a constexpr three-way comparison operator in C++20 by extending the MyInt class. Learn to enable comparisons between MyInt and int in all combinations, minimizing code by leveraging compiler-generated and user-defined operators. This lesson helps you grasp elegant and efficient operator overloading techniques for custom types.

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Solution

C++
#include <compare>
#include <iostream>
class MyInt { 
    public:
        constexpr explicit MyInt(int val): value{val} { }
        auto operator<=>(const MyInt& rhs) const = default;
        constexpr auto operator<=>(const int& rhs) const { 
            return value <=> rhs;
        }
    private:
        int value;
};
template<typename T,typename T2> 
constexpr bool isLessThan(const T& lhs,const T2& rhs) {
    return lhs < rhs; 
}
int main() {
    std::cout << std::boolalpha << '\n';
    constexpr MyInt myInt2011(2011);
    constexpr MyInt myInt2014(2014);
    constexpr int int2011(2011);
    constexpr int int2014(2014);
    std::cout << "isLessThan(myInt2011, myInt2014): "
              << isLessThan(myInt2011, myInt2014) << '\n';
    std::cout << "isLessThan(int2011, myInt2014): "
              << isLessThan(int2011, myInt2014) << '\n';
    std::cout << "isLessThan(myInt2011, int2014): "
              << isLessThan(myInt2011, int2014) << '\n'; 
              
    constexpr auto res = isLessThan(myInt2011, int2014); 
    
    std::cout << '\n'; 
}

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