[Base] Added a map inserting function

BaseLib/uniqueInsert.h

@@ -27,6 +27,20 @@ void uniquePushBack(Container& container, typename Container::value_type const&
         container.push_back(element);
 }
 
+//! Inserts the given \c key with the given \c value into the \c map if an entry with the
+//! given \c key does not yet exist; otherwise an \c error_message is printed and the
+//! program is aborted.
+template<typename Map, typename Key, typename Value>
+void insertMapIfKeyUniqueElseError(
+    Map& map, Key const& key, Value&& value,
+    std::string const& error_message)
+{
+    auto const inserted = map.emplace(key, std::forward<Value>(value));
+    if (!inserted.second) { // insertion failed, i.e., key already exists
+        OGS_FATAL("Failed insert %s. Key already exists.",
+                  error_message.c_str());
+    }
+}
 
 //! Inserts the given \c key with the given \c value into the \c map if an entry with the
 //! given \c key does not yet exist; otherwise an \c error_message is printed and the