From: transfire@...
Date: 2006-07-07T06:09:08+09:00
Subject: Re: Achieving Equality


Chris Hulan wrote:

> I suggest modifying your == method to:
> def ==( other )
>     #p "#{@read.call} == #{other.inspect}"
>     if other.kind_of?(RWDelegator)
>       other == @read.call
>     else
>       @read.call == other
>     end
> end
>
> To compare to other objects you can:
> 1) write conversion methods (i.e. to_s) and than convert the RWDelegator
> to the appropriate type when comparing (i.e. rwd.to_s == "1")
>
> 2) re-write the conversion methods of the other classes to handle your
> RWDelegator class appropriately:
> class String
>   alias old== ==
>   def ==(other)
>     if other.kind_of(RWDelegator)
>       other == self
>     else
>       old==(other)
>     end
>   end
>

Thanks! Your suggestions gave me this idea:

class RWDelegator

  def initialize( write, &read )
    @read = read
    @write = write

    read_class = @read.call.object_class

    unless read_class.method_defined?(:eq_with_rwdelegator?)
      read_class.class_eval %{
        def eq_with_rwdelegator?( other )
          if RWDelegator === other
            other == self
          else
            eq_without_rwdelegator?(other)
          end
        end
        alias_method :eq_without_rwdelegator?, :==
        alias_method :==, :eq_with_rwdelegator?
      }
    end
  end

  ...

T.