From: Simon Strandgaard <neoneye@...>
Date: 2004-04-03T01:34:21+09:00
Subject: Re: parent of TrueClass, FalseClass

On Fri, 02 Apr 2004 09:24:45 -0700, Ara.T.Howard wrote:

> On Fri, 2 Apr 2004, Yukihiro Matsumoto wrote:
> 
>> Hi,
>> 
>> In message "parent of TrueClass, FalseClass"
>>     on 04/04/02, "Ara.T.Howard" <Ara.T.Howard@noaa.gov> writes:
>> 
>> |any good reason these would not have a common parent Bool or something?
>> 
>> Is there any good reason to have a common parent Bool, where true and
>> false are only representations values of truth.
>> 
>> 							matz.
> 
> well - no, except that i'm sure alot of code would break if we pulled out
> TrueClass and FalseClass.  i guess you surely could have something like
> 
>   class Bool
>     TRUE = new
>     FALSE = new
>     ...
>   end
> 
> if done from the start this would make some sort of sense.  i just find it a
> bit suprising that true and false, which are both representations values of
> truth, are not related in anyway (duck type, module inclusion, parent class,
> etc) and it is difficult (verbose) in ruby code to ask
> 
>   "is this a truth value"
> 
> i realize ruby is moving more towards duck typing.  but considering that - how
> to you duck type a truth value?  i mean, which method must something
> respond_to? in order to be a bool?  could it be useful if there was one?
> 
>   class Foo
>     include Truth
> 
>     def initialize arg
>       @bar = true if arg == 42
>     end
> 
>     def truth           # all logical operations derived from this
>       true unless @bar 
>     end
>   end
> 
>   xor = Foo.new(0) ^ Foo.new(42) 
> 


How about  (untested)

Then it would be easy to add a Maybe class ;-)

server> cat a.rb 
module Boolean
        class Base
                include Singleton
        end
        class True < Base
                def to_s; "true" end
        end
        class False < Base
                def to_s; "false" end
        end
end # module Boolean

TRUE  = Boolean::True.instance
FALSE = Boolean::False.instance
server>


--
Simon Strandgaard