From: Joel VanderWerf <vjoel@...>
Date: 2004-06-18T10:15:44+09:00
Subject: Re: How to make generic #== method?

Zakaria wrote:
> Hi,
> 
> Currently I got many simple class which is just a simple record-like.
> An example
> -----------------------------------
> class LoopTag # :nodoc:
>   attr_reader :param
>   attr_reader :contents
> 
>   def initialize(param)
>     @param, @contents = param, []
>   end
> 
>   def ==(other)
>     return false unless other.class == self.class
>     return other.param == @param && other.contents == @contents
>   end
> end
> ------------------------------------
> and I got a couple more class like this.
> 
> Is there a way to make a generic #== or some Module that I can include ?

One way I've done it is this:

module ContentEquality
   def hash
     content.hash
   end

   def eql?(other)
     content.eql? other.content
   end

   def ==(other)
     # self.class == other.class and # optional
     content == other.content
   end
end

Just include the module and define a content method that returns 
something like and array of objects that are significant for comparison 
purposes:

class LoopTag
   include ContentEquality

   def content
     [@param, @contents]
   end
end

Another way might be to iterate over a list of instance variables (or 
all of 'em, if that's what you want).