Question

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 information between them it would be great if Ruby code could be used.

Answer 1

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.