def implementation(*selectors)
      selectors << :auto if selectors.empty?
      Implementation::Registry::Finder.new(@implementations, selectors)
    end
def implementation(*selectors)
      selectors << :auto if selectors.empty?
      Implementation::Registry::Finder.new(@implementations, selectors)
    end
Used to find a suitable implementation
 @api public
 @param [*selectors] zero or more selectors to use for finding an
   implementation of this interface. If none is given, :auto is assumed.
 @return [Implementation::Registry::Finder]