Three-way comparison spaceship <=> operators for Cord.

This is portable because cord already has `operator<` etc., which will be unaffected. This just allows C++ >= 20 users to explicitly call `operator<=>`.

PiperOrigin-RevId: 646951415
Change-Id: I1432e224bd5dc09b99d56a1d27e95078463adf45

1 files changed, 33 insertions, 0 deletions

diff --git a/absl/strings/cord.h b/absl/strings/cord.h
index 0d8d7007..c68b6f10 100644
--- a/absl/strings/cord.h
+++ b/absl/strings/cord.h
@@ -96,6 +96,7 @@
 #include "absl/strings/internal/resize_uninitialized.h"
 #include "absl/strings/internal/string_constant.h"
 #include "absl/strings/string_view.h"
+#include "absl/types/compare.h"
 #include "absl/types/optional.h"
 
 namespace absl {
@@ -849,6 +850,38 @@ class Cord {
   friend bool operator==(const Cord& lhs, const Cord& rhs);
   friend bool operator==(const Cord& lhs, absl::string_view rhs);
 
+#ifdef __cpp_impl_three_way_comparison
+
+  // Cords support comparison with other Cords and string_views via operator<
+  // and others; here we provide a wrapper for the C++20 three-way comparison
+  // <=> operator.
+
+  static inline std::strong_ordering ConvertCompareResultToStrongOrdering(
+      int c) {
+    if (c == 0) {
+      return std::strong_ordering::equal;
+    } else if (c < 0) {
+      return std::strong_ordering::less;
+    } else {
+      return std::strong_ordering::greater;
+    }
+  }
+
+  friend inline std::strong_ordering operator<=>(const Cord& x, const Cord& y) {
+    return ConvertCompareResultToStrongOrdering(x.Compare(y));
+  }
+
+  friend inline std::strong_ordering operator<=>(const Cord& lhs,
+                                                 absl::string_view rhs) {
+    return ConvertCompareResultToStrongOrdering(lhs.Compare(rhs));
+  }
+
+  friend inline std::strong_ordering operator<=>(absl::string_view lhs,
+                                                 const Cord& rhs) {
+    return ConvertCompareResultToStrongOrdering(-rhs.Compare(lhs));
+  }
+#endif
+
   friend absl::Nullable<const CordzInfo*> GetCordzInfoForTesting(
       const Cord& cord);