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Can object instances know each other's current states?

I have 3 objects:

  • Parser
  • ParserState - a state machine that tracks the current state and transitions between states
  • ParserDefinitions - it reads from a json file and supplies the regexes of a given state, as well as some other rules that govern how the parser operates

ParserState and ParserDefinitions are both subclasses (?) of Parser and are defined as Parser::ParserState and Parser::ParserDefinitions. It would be great if the ParserState object could have access to the current instance of ParserDefinitions and vice versa. Is this possible, or does it imply that they should actually be combined in to one class?

Btw, I am using Ruby so if it is possible that they share instance in开发者_如何学Goformation between them it would be great if Ruby code could be used.


  1. Those are not subclasses, they are simply namespaced under the class. This provides no linkage between the class objects.

  2. The way that object A accesses the state of object B is by invoking methods on object B and looking at the return values. It seems that the only issue here is how to make object A know about object B.

  3. You have capitalized the names of these as though they are modules or classes, but you seem to be referring to them as instances. Are these singleton objects, or does (for example) a Parser instance create both ParserStart and ParserDefinitions instances? Assuming that the latter is the case:

    class Parser
      attr_accessor :states, :defns
      def initialize
        self.states = ParserStates.new( self )
        self.defns  = ParserDefinitions.new( self )
      end
    end
    
    class Parser::ParserStates
      attr_accessor :parser
      def initialize( parent_parser )
        self.parser = parent_parser
      end
      def defns
        parser.defns
      end
    end
    
    class Parser::ParserDefinitions
      attr_accessor :parser
      def initialize( parent_parser )
        self.parser = parent_parser
      end
      def states
        parser.states
      end
    end
    

    Given the above, where each 'child' object knows about its 'parent' and the parent exposes accessors to the children, all objects can talk to one another.

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