From 30343c8d3eee26d0f4ca8dd84c68d1350304021a Mon Sep 17 00:00:00 2001
From: Mike Krinkin <krinkin.m.u@gmail.com>
Date: Sat, 28 Mar 2015 09:58:27 +0300
Subject: [PATCH] Derive equal_to from compare/less functors.

For unordered lists it is possible to derive equal_to from compare
or less functors. This patch fixes make_equal_to so that it
returns equal_to if it is specified, else if compare is specified
it derives equal_to from compare functor, otherwise it derives
equal_to from less functor.
---
 cds/opt/compare.h | 42 +++++++++++++++++++++++++++++++++++++++---
 1 file changed, 39 insertions(+), 3 deletions(-)

diff --git a/cds/opt/compare.h b/cds/opt/compare.h
index 3bcfc961..1243f5be 100644
--- a/cds/opt/compare.h
+++ b/cds/opt/compare.h
@@ -244,16 +244,52 @@ namespace cds { namespace opt {
 
     //@cond
     namespace details {
+        template <typename Compare>
+        struct make_equal_to_from_compare
+        {
+            typedef Compare compare_functor;
+
+            template <typename T, typename Q>
+            bool operator()( T const& t, Q const& q ) const
+            {
+                compare_functor cmp;
+                return cmp(t, q) == 0;
+            }
+        };
+
+        template <typename Less>
+        struct make_equal_to_from_less
+        {
+            typedef Less less_functor;
+
+            template <typename T, typename Q>
+            bool operator()( T const& t, Q const& q ) const
+            {
+                less_functor less;
+                return !less(t, q) && !less(q, t);
+            }
+        };
+
         template <typename T, typename Traits, bool Forced = true>
         struct make_equal_to
         {
             typedef typename Traits::equal_to equal_to;
+            typedef typename Traits::compare  compare;
+            typedef typename Traits::less     less;
 
             typedef typename std::conditional<
                 std::is_same< equal_to, opt::none >::value,
-                typename std::conditional< Forced, std::equal_to<T>, opt::none >::type,
-                equal_to
-            >::type type;
+                typename std::conditional<
+                    std::is_same< compare, opt::none >::value,
+                    typename std::conditional<
+                        std::is_same< less, opt::none >::value,
+                        typename std::conditional<
+                            Forced,
+                            std::equal_to<T>,
+                            opt::none >::type,
+                        make_equal_to_from_less< less > >::type,
+                    make_equal_to_from_compare< compare > >::type,
+                equal_to >::type type;
         };
     }
     //@endcond
-- 
2.34.1