From: Mark Probert <probertm@...>
Date: 2002-02-23T04:19:19+09:00
Subject: dispatching and class references


Thank you for everyone for helping me with my dispatch
query the other day.  Now fro part 2 :-)

It seems that ruby returns object values by reference.
Is there any way to return the value?  I would like the
pattern, stored in Sym::val to be treated as a template
and retain its value ('xxx') over each dispatch call.

So:


     class Sym
         attr_reader :sym, :val
         def initialize(sym, val)
             @sym = sym
             @val = val
         end
         def to_s
             "sym = #{@sym} val=#{@val}"
         end
     end

     class Bob

         @@dtbl = {
             'a' => Sym.new(:do_a, 'this is a string: xxx'),
             'b' => Sym.new(:do_b, 'so is this: xxx')
         }

         def do_a(msg=nil)
             puts "a --> #{msg}"
         end

         def do_b(msg=nil)
             puts "b --> #{msg}"
         end

         def dispatch(ref=nil)
             if @@dtbl[ref]
                 obj = @@dtbl[ref]
                 s = obj.val
                 s.sub!(/xxx/, '123')
                 send obj.sym, obj.val
             else
                 puts "--> unknown ref (#{ref})"
             end
         end

         def prntbl
             @@dtbl.keys.each { |k| puts @@dtbl[k] }
         end
     end

         irb(main):001:0> b = Bob.new
         #<Bob:0xa0b8cf0>

         irb(main):002:0> b.prntbl
         sym = do_a val=this is a string: xxx
         sym = do_b val=so is this: xxx
         ["a", "b"]

         irb(main):003:0> b.dispatch('a')
         a --> this is a string: 123
         nil

         irb(main):004:0> b.prntbl
         sym = do_a val=this is a string: 123  # <-- the sub! has changed 
obj.val
         sym = do_b val=so is this: xxx
         ["a", "b"]


Regards,



-mark.