[ruby-talk:01817] Re: Objects nested sometimes.

On 14 Mar 2000, Dave Thomas wrote:

> Hugh Sasse Staff Elec Eng <[e-mail]> writes:
> 
> > I asked someone about how to do this neatly on an OO way, and they 
> > said, "have the ports contain references to the voltages".  However,
> > I cannot see any reference or pointer types in ruby.  Is there a
> > neat way of doing this in ruby?
> 
> In Ruby, variables _are_ references to objects, so you could implement 
> your port with (say) an array of voltages, and the node as an array of 
> ports.
> 
> Say you have
> 
>    v1 = "Fred"
>    v2 = v2

Ah! looking at the FAQ again, this is 2.1 and 7.4.  
> 
> Then in terms of memory and references, what you've done is assigned a 
> reference to the String "Fred" to v2, and then copied that reference
> to v2.
> 
> 
>     v1 ---------
>                 \    __String____
>                  -->|            |
>                  -->|  Fred      |
>                 /   |____________|
>     v2 ---------
> 
> (sorry, I missed the ASCII art class at school)

	That is vary clear.  Thank you.  So when I create my ports
	within my node, I can pass in a pointer to the node...

	class Port
            def new(parent, portnum)
               initialise(parent, portnum)
            end
            def initialize(parent, portnum)
               @parent = parent	
               case portnum
               when 1 
                  @v1 = @parent.vxy1
                  @v2 = @parent.vxz1
               when 2
                  @v1 = @parent.vyx1
                  @v2 = @parent.vyz1
> 	       # etc
            end
        end

        class Node
             def new()
               ...
             end
             def initialize()
                 # setup the voltages...
                 @vxy1 = 0.0
                 attr("vxy1", true)
                 ...
                 # setup the ports passing myself as parent...
                 port1 = Port.new(self,1)
                 port2 = Port.new(self,2)
                 #etc
             end
        end

	sort of thing?  I'm just a bit unsure about the instance
	variables in both types -- I know I can make them public with
	attr() but that creates *functions* to access them[?], so will 
	that mean that the port cannot point to the parent's variables,
	or not?  I will have several nodes and several ports, so it
	must be the case that the voltages (for a node or a port) are
	not shared across all instances of the same type (node or
	port).  Hence my question about instance variables.


	Thank you,

> Regards
> 
> 
> Dave
> 
	Hugh
	[e-mail]