Initial Commit

- add implementation of three way comparison in c++17 and c++20

.gitignore

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+.vscode/
+build/

CMakeLists.txt

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+cmake_minimum_required(VERSION 3.17.0)
+project(cpp20_demo)
+
+include(CTest)
+enable_testing()
+
+add_subdirectory(cpp17)
+add_subdirectory(cpp20)
+
+add_executable(cpp20_demo main.cpp)
+
+target_link_libraries(cpp20_demo
+    PUBLIC
+        cpp17_demo_lib
+        cpp20_demo_lib
+)

README.md

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+# cpp20_demo
+
+Demo of new features of standard C++20. This repo would contain some comparison of implementations between C++20 and its prior standard C++17.

cpp17/CMakeLists.txt

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+set(CMAKE_CXX_STANDARD 17)
+
+add_library(cpp17_demo_lib STATIC
+    ThreeComp.cpp
+)

cpp17/ThreeComp.cpp

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+#include "ThreeComp.hpp"
+
+#include <iostream>
+
+namespace cpp17
+{
+    void threeCompDemo()
+    {
+        constexpr double foo = -0.0;
+        constexpr double bar = 0.0;
+
+        std::cout << "cpp17: ";
+
+        if (foo < bar)
+        {
+            std::cout << "-0 is less than 0";
+        }
+        else if (foo > bar)
+        {
+            std::cout << "-0 is greater than 0";
+        }
+        else // (foo == bar)
+        {
+            std::cout << "-0 and 0 are equal";
+        }
+
+        std::cout << "\n";
+    }
+
+    struct Point
+    {
+        int x;
+        int y;
+        bool operator<(const Point &other) const
+        {
+            if (x < other.x)
+            {
+                return true;
+            }
+
+            if (y >= other.y)
+            {
+                return false;
+            }
+
+            return true;
+        }
+        bool operator==(const Point &other) const
+        {
+            return (x == other.x) && (y == other.y);
+        }
+        bool operator>(const Point &other) const
+        {
+            if (x > other.x)
+            {
+                return true;
+            }
+
+            if (y <= other.y)
+            {
+                return false;
+            }
+
+            return true;
+        }
+    };
+    // compiler generates all six two-way comparison operators
+
+    void threeCompOperatorOverloadDemo()
+    {
+        constexpr Point A{1, 1};
+        constexpr Point B{2, 1};
+
+        std::cout << "cp20: ";
+
+        if (A < B)
+        {
+            std::cout << "A is less than B";
+        }
+        else if (A > B)
+        {
+            std::cout << "A is greater than B";
+        }
+        else // (A == B)
+        {
+            std::cout << "A and B are equal";
+        }
+
+        std::cout << "\n";
+    }
+}

cpp17/ThreeComp.hpp

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+#pragma once
+
+namespace cpp17
+{
+    void threeCompDemo();
+    void threeCompOperatorOverloadDemo();
+}

cpp20/CMakeLists.txt

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+set(CMAKE_CXX_STANDARD 20)
+
+add_library(cpp20_demo_lib STATIC
+    ThreeWayComp.cpp
+)

cpp20/ThreeWayComp.cpp

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+#include "ThreeWayComp.hpp"
+
+#include <compare>
+#include <iostream>
+
+namespace cpp20
+{
+    void threeWayCompDemo()
+    {
+        constexpr double foo = -0.0;
+        constexpr double bar = 0.0;
+
+        constexpr auto res = (foo <=> bar);
+
+        std::cout << "cp20: ";
+
+        if (res < 0)
+        {
+            std::cout << "-0 is less than 0";
+        }
+        else if (res > 0)
+        {
+            std::cout << "-0 is greater than 0";
+        }
+        else // (res == 0)
+        {
+            std::cout << "-0 and 0 are equal";
+        }
+
+        std::cout << "\n";
+    }
+
+    struct Point
+    {
+        int x;
+        int y;
+        auto operator<=>(const Point &) const = default;
+    };
+    // compiler generates all six two-way comparison operators
+
+    void threeWayOperatorOverloadDemo()
+    {
+        constexpr Point A{1, 1};
+        constexpr Point B{2, 1};
+
+        constexpr auto res = (A <=> B);
+
+        std::cout << "cp20: ";
+
+        if (res < 0)
+        {
+            std::cout << "A is less than B";
+        }
+        else if (res > 0)
+        {
+            std::cout << "A is greater than B";
+        }
+        else // (res == 0)
+        {
+            std::cout << "A and B are equal";
+        }
+
+        std::cout << "\n";
+    }
+}

cpp20/ThreeWayComp.hpp

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+#pragma once
+
+namespace cpp20
+{
+    void threeWayCompDemo();
+    void threeWayOperatorOverloadDemo();
+}

main.cpp

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+#include "cpp17/ThreeComp.hpp"
+#include "cpp20/ThreeWayComp.hpp"
+
+#include <iostream>
+
+int main(int, char **)
+{
+    cpp17::threeCompDemo();
+    cpp20::threeWayCompDemo();
+    cpp17::threeCompOperatorOverloadDemo();
+    cpp20::threeWayOperatorOverloadDemo();
+}