From: Mohammad Khan <mkhan@...>
Date: 2004-11-12T00:28:35+09:00
Subject: Re: true? & false?

The main reason I brought up this issue is:
to make differentiation between "a value in boolean context" and "its
real value"

Example,
a = Foo.new
b = nil

a is *true* in boolean context but it is not really a TrueClass or true.
again, b is 'false' in a boolean context but it is not a FalseClass or
false.

thats why, I proposed to have 

class Object
   def true?
      return ( (self == true) or (self === TrueClass) )
   end

   def false?
      return ( (self == false) or (self === FalseClass) )
   end
end

so.. again for the above examples:
puts "a is true in boolean context" if a
puts "a is really a *true*" if a.true?


puts "b is false in boolean context" if not b
puts "b is really *false*" if b.false?

if you find true? and false? is not readable or more complex to use, you
might like to write:
puts "a is really a *true*" if a == true
puts "b is really a *false*" if b == false


Thanks again,
Mohammad


On Thu, 2004-11-11 at 08:08, Robert Klemme wrote:
> "Jean-Hugues ROBERT" <jean_hugues_robert@yahoo.com> schrieb im Newsbeitrag
> news:6.0.1.1.0.20041111082218.040feec0@pop.mail.yahoo.com...
> > Hi,
> >
> > I think things should stay the way they are, here is
> > why.
> >
> > Things are a little complex about truthness/falseness.
> > One has to distinguish the "value" of an object from
> > its "truthness".
> 
> I'm not sure whether I follow you here: an object *is* the value.  There
> is no such thing as a value that is distinct from the object.  An object
> is interpreted as in boolean contexts according to certain rules (false
> and nil => false, all others true); you could call this convention
> "truthness", yes.
> 
> > Only nil and false are "false" from a "truthness"
> > perspective. All other objects are "true".
> >
> > For true? and false? to be somehow usefull, I first felt
> > that they should relate to the "truthness" of the
> > object, not its "value". That is very different from
> > nil? (it checks the value of the object, only The nil
> > object is nil?).
> >
> > This leads to:
> > class Object
> >   def true?  ; true      ; end
> >   def false? ; not true? ; end
> > end
> > class NilClass
> >   def true?  ; false     ; end
> > end
> > class FalseClass
> >   def true?  ; false     ; end
> > end
> 
> You can simplify this to
> 
> class Object
>   def true?; self end
>   def false?; not true? end
> end
> 
> because it's the standard convention.  Basically this adds one level of
> indirection (the method call).
> 
> > Usage: 1 - Checking truthness
> >   if some_thing.true? then
> >     xxx
> >   end
> > Usage: 2 - Checking value
> >   if some_thing == true then
> >     xxx
> >   end
> >
> > On the other hand, one may consider that
> > checking the value is what matters most,
> > versus checking the truthness.
> 
> I never felt the need for "some_thing == true".  In which cases do you
> need this?
> 
> > This leads to:
> > class Object
> >   def true?  ; false ; end
> >   def false? ; false ; end
> > end
> > class TrueClass
> >   def true?  ; true  ; end
> > end
> > class FalseClass
> >   def false? ; true  ; end
> > end
> 
> You can simplify this, too:
> 
> class Object
>   def true?; TrueClass === self end
>   def false?; FalseClass === self end
> end
> 
> > Usage: 1 - Checking the truthness
> >   if some_thing then
> >     xxx
> >   end
> > Usage: 2 - Checking the value
> >   if some_thing.true? then
> >     xxx
> >   end
> >
> > Solution 2 (checking values) leads to
> > code that is slightly smaller (less characters).
> > Which is probably a good thing by itself.
> > However, I think that it is fairly unreadable.
> 
> Yep.  I find this quite irritating.  When I see "if some_thing.true?
> then..." I'd expect the truthness of some_thing to be used, not the
> outcome of the test whether some_thing is actually the instance 'true'.
> 
> > As a conclusion, I think that the status quo
> > is the best solution. Instead of a hard to
> > understand true?/false?, let's keep an explicit
> > xxx == true when value matters instead of
> > truthness.
> 
> .... or "TrueClass === xxx" for that matter.  Yes.  Totally agree.
> 
> > My 0.2 Euros.
> 
> Now we got 0.22 EUR. :-)
> 
> Kind regards
> 
>     robert
-- 

Everyone thinks of changing the world,
but no one thinks of changing himself.
                  - Leo Tolstoy