1 files changed, 18 insertions, 8 deletions

@@ -5,6 +5,15 @@
 #include <vector>
 
 template <typename T>
+class DefaultKeyExtract {
+public:
+
+  const T& operator()(const T& val) const {
+    return val;
+  }
+};
+
+template <typename T, typename KeyExtract = DefaultKeyExtract<T>>
 class identifier {
 public:
 
@@ -12,20 +21,21 @@ public:
 
 private:
 
+  using key_type = std::remove_reference_t<std::invoke_result_t<KeyExtract, const T&>>;
   using vector_type = std::vector<value_type>;
 
 public:
 
-  using key_type = typename vector_type::size_type;
+  using id_type = typename vector_type::size_type;
 
-  key_type add(const value_type& val)
+  id_type add(const value_type& val)
   {
-    auto it = ids_.find(val);
+    auto it = ids_.find(KeyExtract()(val));
 
     if (it == std::end(ids_))
     {
-      key_type ret = ids_.size();
-      ids_[val] = ret;
+      id_type ret = ids_.size();
+      ids_[KeyExtract()(val)] = ret;
 
       uniq_.push_back(val);
 
@@ -40,19 +50,19 @@ public:
     ids_.clear();
   }
 
-  inline const value_type& get(key_type i) const
+  inline const value_type& get(id_type i) const
   {
     return uniq_.at(i);
   }
 
-  inline key_type size() const
+  inline id_type size() const
   {
     return uniq_.size();
   }
 
 private:
 
-  std::map<value_type, key_type> ids_;
+  std::map<key_type, id_type> ids_;
   vector_type uniq_;
 };