add observers interface

flat_map.hpp

@@ -44,6 +44,19 @@ namespace flat_hpp
         using reverse_iterator = typename data_type::reverse_iterator;
         using const_reverse_iterator = typename data_type::const_reverse_iterator;
 
+        class value_compare final : public std::binary_function<value_type, value_type, bool> {
+        public:
+            bool operator()(const value_type& l, const value_type& r) const {
+                return compare_(l.first, r.first);
+            }
+        private:
+            friend class flat_map;
+            explicit value_compare(const key_compare& compare)
+            : compare_(compare) {}
+        private:
+            key_compare compare_;
+        };
+
         static_assert(
             std::is_same<typename allocator_type::value_type, value_type>::value,
             "Allocator::value_type must be same type as value_type");
@@ -222,6 +235,14 @@ namespace flat_hpp
             //TODO(BlackMat): implme
             return end();
         }
+
+        key_compare key_comp() const {
+            return compare_;
+        }
+
+        value_compare value_comp() const {
+            return value_compare(compare_);
+        }
     private:
         data_type data_;
         key_compare compare_;

flat_map_tests.cpp

@@ -152,4 +152,10 @@ TEST_CASE("flat_map") {
         s0.upper_bound(30);
         my_as_const(s0).upper_bound(30);
     }
+    SECTION("observers") {
+        using map_t = flat_map<int, unsigned>;
+        map_t s0;
+        my_as_const(s0).key_comp();
+        my_as_const(s0).value_comp();
+    }
 }

flat_set.hpp

@@ -221,6 +221,14 @@ namespace flat_hpp
             //TODO(BlackMat): implme
             return end();
         }
+
+        key_compare key_comp() const {
+            return compare_;
+        }
+
+        value_compare value_comp() const {
+            return value_compare(compare_);
+        }
     private:
         data_type data_;
         key_compare compare_;

flat_set_tests.cpp

@@ -143,4 +143,10 @@ TEST_CASE("flat_set") {
         s0.upper_bound(30);
         my_as_const(s0).upper_bound(30);
     }
+    SECTION("observers") {
+        using set_t = flat_set<int>;
+        set_t s0;
+        my_as_const(s0).key_comp();
+        my_as_const(s0).value_comp();
+    }
 }