Add transparent at()

include/boost/unordered/unordered_flat_map.hpp

@@ -473,6 +473,34 @@ namespace boost {
           std::out_of_range("key was not found in unordered_flat_map"));
       }
 
+      template <class K>
+      typename std::enable_if<
+        boost::unordered::detail::are_transparent<K, hasher, key_equal>::value,
+        mapped_type&>::type
+      at(K&& key)
+      {
+        auto pos = table_.find(std::forward<K>(key));
+        if (pos != table_.end()) {
+          return pos->second;
+        }
+        boost::throw_exception(
+          std::out_of_range("key was not found in unordered_flat_map"));
+      }
+
+      template <class K>
+      typename std::enable_if<
+        boost::unordered::detail::are_transparent<K, hasher, key_equal>::value,
+        mapped_type const&>::type
+      at(K&& key) const
+      {
+        auto pos = table_.find(std::forward<K>(key));
+        if (pos != table_.end()) {
+          return pos->second;
+        }
+        boost::throw_exception(
+          std::out_of_range("key was not found in unordered_flat_map"));
+      }
+
       BOOST_FORCEINLINE mapped_type& operator[](key_type const& key)
       {
         return table_.try_emplace(key).first->second;

include/boost/unordered/unordered_map.hpp

@@ -973,13 +973,23 @@ namespace boost {
 
       mapped_type& operator[](const key_type&);
       mapped_type& operator[](BOOST_RV_REF(key_type));
+
       template <class Key>
       typename boost::enable_if_c<detail::are_transparent<Key, H, P>::value,
         mapped_type&>::type
       operator[](BOOST_FWD_REF(Key) k);
+
       mapped_type& at(const key_type&);
       mapped_type const& at(const key_type&) const;
 
+      template <class Key>
+      typename boost::enable_if_c<detail::are_transparent<Key, H, P>::value,
+        mapped_type&>::type at(BOOST_FWD_REF(Key) k);
+
+      template <class Key>
+      typename boost::enable_if_c<detail::are_transparent<Key, H, P>::value,
+        mapped_type const&>::type at(BOOST_FWD_REF(Key) k) const;
+
       // bucket interface
 
       size_type bucket_count() const BOOST_NOEXCEPT
@@ -2260,6 +2270,42 @@ namespace boost {
         std::out_of_range("Unable to find key in unordered_map."));
     }
 
+    template <class K, class T, class H, class P, class A>
+    template <class Key>
+    typename boost::enable_if_c<detail::are_transparent<Key, H, P>::value,
+      typename unordered_map<K, T, H, P, A>::mapped_type&>::type
+    unordered_map<K, T, H, P, A>::at(BOOST_FWD_REF(Key) k)
+    {
+      typedef typename table::node_pointer node_pointer;
+
+      if (table_.size_) {
+        node_pointer p = table_.find_node(boost::forward<Key>(k));
+        if (p)
+          return p->value().second;
+      }
+
+      boost::throw_exception(
+        std::out_of_range("Unable to find key in unordered_map."));
+    }
+
+    template <class K, class T, class H, class P, class A>
+    template <class Key>
+    typename boost::enable_if_c<detail::are_transparent<Key, H, P>::value,
+      typename unordered_map<K, T, H, P, A>::mapped_type const&>::type
+    unordered_map<K, T, H, P, A>::at(BOOST_FWD_REF(Key) k) const
+    {
+      typedef typename table::node_pointer node_pointer;
+
+      if (table_.size_) {
+        node_pointer p = table_.find_node(boost::forward<Key>(k));
+        if (p)
+          return p->value().second;
+      }
+
+      boost::throw_exception(
+        std::out_of_range("Unable to find key in unordered_map."));
+    }
+
     template <class K, class T, class H, class P, class A>
     typename unordered_map<K, T, H, P, A>::size_type
     unordered_map<K, T, H, P, A>::bucket_size(size_type n) const