def struct_namespace(namespace = Undefined)
      if namespace.equal?(Undefined)
        options[:struct_namespace]
      else
        with(struct_namespace: namespace)
      end
    end
def struct_namespace(namespace = Undefined)
      if namespace.equal?(Undefined)
        options[:struct_namespace]
      else
        with(struct_namespace: namespace)
      end
    end
Get factories with a custom struct namespace

 @example
   EntityFactory = MyFactory.struct_namespace(MyApp::Entities)

   EntityFactory[:user]
   # => #<MyApp::Entities::User id=2 ...>

 @param [Module] namespace

 @return [Factories]

 @api public