From d95c6f9b05ddfdb428e06651e3380d8612c43d52 Mon Sep 17 00:00:00 2001
From: BlackMATov <blackmatov@gmail.com>
Date: Sat, 4 May 2019 12:45:22 +0700
Subject: [PATCH] add observers interface

---
 flat_map.hpp       | 21 +++++++++++++++++++++
 flat_map_tests.cpp |  6 ++++++
 flat_set.hpp       |  8 ++++++++
 flat_set_tests.cpp |  6 ++++++
 4 files changed, 41 insertions(+)

diff --git a/flat_map.hpp b/flat_map.hpp
index c882c9f..7c6ad6d 100644
--- a/flat_map.hpp
+++ b/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_;
diff --git a/flat_map_tests.cpp b/flat_map_tests.cpp
index d1d8283..78564e1 100644
--- a/flat_map_tests.cpp
+++ b/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();
+    }
 }
diff --git a/flat_set.hpp b/flat_set.hpp
index f985ada..d9bf478 100644
--- a/flat_set.hpp
+++ b/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_;
diff --git a/flat_set_tests.cpp b/flat_set_tests.cpp
index f251a15..d360cd4 100644
--- a/flat_set_tests.cpp
+++ b/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();
+    }
 }