From 9927206e62ac74b1c01feec4141a09777eb18cbd Mon Sep 17 00:00:00 2001
From: Tim Blechmann <tim@klingt.org>
Date: Wed, 4 Oct 2023 09:42:23 +0800
Subject: [PATCH] implement threeway comparison

---
 include/semver.hpp | 16 ++++++++++++++++
 test/test.cpp      | 27 +++++++++++++++++++++++++++
 2 files changed, 43 insertions(+)

diff --git a/include/semver.hpp b/include/semver.hpp
index 5f1d9d6..459f8df 100644
--- a/include/semver.hpp
+++ b/include/semver.hpp
@@ -76,6 +76,11 @@
 #  pragma clang diagnostic ignored "-Wmissing-braces" // Ignore warning: suggest braces around initialization of subobject 'return {first, std::errc::invalid_argument};'.
 #endif
 
+#if __cpp_impl_three_way_comparison >= 201907L
+#include <compare>
+#endif
+
+
 namespace semver {
 
 enum struct prerelease : std::uint8_t {
@@ -482,6 +487,17 @@ struct version {
   return lhs.compare(rhs) <= 0;
 }
 
+#if __cpp_impl_three_way_comparison >= 201907L
+[[nodiscard]] constexpr std::strong_ordering operator<=>(const version& lhs, const version& rhs) {
+  int compare = lhs.compare(rhs);
+  if ( compare == 0 )
+    return std::strong_ordering::equal;
+  if ( compare > 0 )
+    return std::strong_ordering::greater;
+  return std::strong_ordering::less;
+}
+#endif
+
 [[nodiscard]] constexpr version operator""_version(const char* str, std::size_t length) {
   return version{std::string_view{str, length}};
 }
diff --git a/test/test.cpp b/test/test.cpp
index fb0172f..a898c3e 100644
--- a/test/test.cpp
+++ b/test/test.cpp
@@ -406,6 +406,33 @@ TEST_CASE("operators") {
     }
   }
 
+#if __cpp_impl_three_way_comparison >= 201907L
+  SECTION("operator <=>") {
+    constexpr version v1{1, 2, 3, prerelease::rc, 4};
+    constexpr version v2{1, 2, 3};
+    constexpr version v3{1, 2, 3};
+    REQUIRE(v1 <=> v1 == std::strong_ordering::equal);
+    REQUIRE(v2 <=> v3 == std::strong_ordering::equal);
+
+    auto validate_threeway_compare = [] (auto v1, auto v2) {
+      if (v1 < v2)
+        REQUIRE(v1 <=> v2 == std::strong_ordering::less);
+      else if (v1 > v2)
+        REQUIRE(v1 <=> v2 == std::strong_ordering::greater);
+      else if (v1 == v2)
+        REQUIRE(v1 <=> v2 == std::strong_ordering::equal);
+    };
+
+    for (std::size_t i = 1; i < versions.size(); ++i) {
+      for (std::size_t j = 1; j < i; ++j) {
+        version v = versions[i - j];
+        validate_threeway_compare(versions[i - j], versions[i]);
+        validate_threeway_compare(v, versions[i - j]);
+      }
+    }
+  }
+#endif
+
   SECTION("operator _version") {
     constexpr version v = "1.2.3-rc.4"_version;
     static_assert(v == version{1, 2, 3, prerelease::rc, 4});