From: Mohammad Khan <mkhan@...>
Date: 2004-11-12T05:41:50+09:00
Subject: Re: true? & false?

On Thu, 2004-11-11 at 14:50, Austin Ziegler wrote:
> On Fri, 12 Nov 2004 00:28:35 +0900, Mohammad Khan
> <mkhan@lextranet.com> wrote:
> > The main reason I brought up this issue is: to make
> > differentiation between "a value in boolean context" and "its real
> > value"
> 
> Why? This is the ultimate question that I don't think has been
> answered at all. Why is #true? and #false superior to explicit
> tests? Note that I'm not referring to the alternative directions
> inspired by your post (e.g., #if_true and #if_false), but your
> suggestion that "foo.true?" is better than "foo == true".
> 
> > class Object
> >   def true?
> >     return ( (self == true) or (self === TrueClass) )
> >   end
> >
> >   def false?
> >     return ( (self == false) or (self === FalseClass) )
> >   end
> > end
> 
> This is improperly written. +true+, +false+, and +nil+ are the only
> possible values of TrueClass, FalseClass, and NilClass,

Yes, I wrote it improperly, sorry about that.

class Object
    def true?
        return self == true
    end

    def false?
        return self == false
    end
end

> respectively. Thus, self == true and TrueClass === self (note the
> inversion of parameters on the call to #===) are the same test. You
> can more efficiently write what you want as:
> 
>   class Object
>     def true?
>       false
>     end
> 
>     def false?
>       false
>     end
>   end
> 

You might noticed from my previous posting, the reason to I want to have
#true? and #false?

Example:
a = true
b = false

using my 'class Object'
a.true? -> true
b.false? -> true

using your 'class Object'
a.true? -> false
b.false? -> false
which are wrong according to my proposed #true? and #false?


>   class TrueClass
>     def true?
>       true
>     end
>   end
> 
>   class FalseClass
>     def false?
>       true
>     end
>   end
> 
> (This is, more or less, how nil? is written. Object#nil? returns
> false; NilClass#nil? returns true.)
> 
> > so.. again for the above examples:
> > puts "a is true in boolean context" if a
> > puts "a is really a *true*" if a.true?
> 
> Why is this better than "if a == true"

I think, its a personal taste.
I like "a.nil?" more than "a == nil"
same way, I like a.true? than a == true
when I consider 'a' in boolean context.. i write . .. " if a"
when I need to make sure that 'a' is really a 'true'.. I write a.true?,
you might write it a == true.

"We live in a free world"
 ;-)

--
Mohammad


> 
> > puts "b is false in boolean context" if not b
> 
> Try "unless b".
> 
> -austin
> --
> Austin Ziegler * halostatue@gmail.com
>                * Alternate: austin@halostatue.ca