A few weeks ago on master I was able to use factory in my _instanceof Yaml service declarations. This was useful because all instances of DoctrineRepository need the same factory call. Without it, all DoctrineRepositories have to duplicate the same factory line. The purpose of _instanceof to reduce duplication would be better served if we could use factory.

@nicolas-grekas I edited DependencyInjection/Loader/YamlFileLoader and added 'factory' => 'factory' to the $instanceofKeywords array and it seemed to work. Any drawbacks? Better solutions?