Check objects inside 'generic_factory' using 'T::check()' function

src/generic_factory.h

@@ -35,6 +35,9 @@ can be by it to implement its interface.
   - a `was_loaded` member of type `bool`, which must have the value `false` before
     the first call to `load`.
 
+  The type can also have:
+  - a 'check()' function (to run `generic_factory::check()` on all objects)
+
   Those things must be visible from the factory, you may have to add this class as
   friend if necessary.
 
@@ -254,6 +257,14 @@ class generic_factory
             map[result.id] = cid;
             return result;
         }
+        /**
+         * Checks loaded/inserted objects for consistency
+         */
+        void check() const {
+            for( const T &obj : list ) {
+                obj.check();
+            }
+        }
         /**
          * Returns the number of loaded objects.
          */

src/mapdata.cpp

@@ -1029,7 +1029,5 @@ void check_furniture_and_terrain()
             debugmsg( "invalid furniture %s for closing %s", f.close.c_str(), f.id.c_str() );
         }
     }
-    for( const ter_t& t : terrain_data.get_all() ) {
-        t.check();
-    }
+    terrain_data.check();
 }