provision of TypeMapProvider to allow lazy creation of type maps only when they are needed

Dapper NET40/SqlMapper.cs

@@ -2154,6 +2154,12 @@ static readonly MethodInfo
                         .Where(p => p.GetIndexParameters().Any() && p.GetIndexParameters()[0].ParameterType == typeof(int))
                         .Select(p => p.GetGetMethod()).First();
 
+        /// <summary>
+        /// Gets type-map for the given type
+        /// </summary>
+        /// <returns>Type map instance, default is to create new instance of DefaultTypeMap</returns>
+        public static Func<Type, ITypeMap> TypeMapProvider = ( Type type ) => new DefaultTypeMap( type );
+
         /// <summary>
         /// Gets type-map for the given type
         /// </summary>
@@ -2170,7 +2176,7 @@ public static ITypeMap GetTypeMap(Type type)
                     map = (ITypeMap)_typeMaps[type];
                     if (map == null)
                     {
-                        map = new DefaultTypeMap(type);
+                        map = TypeMapProvider( type );
                         _typeMaps[type] = map;
                     }
                 }