From: ptkwt@... (Phil Tomson)
Date: 2005-03-29T03:34:46+09:00
Subject: Re: Modifying boolean values

In article <c2c0b66050328082336b5a5e6@mail.gmail.com>,
Farrel Lifson  <farrel.lifson@gmail.com> wrote:
>Hi Rubyists,
>
>Is it possible to somehow ducktype an object so that it behaves like a
>boolean object (ie true or false)?
>
>The problem I'm having at the moment is that I'd like to have a
>modified boolean value so that instead of returning "true" or "false",
>my objects to_s returns "1" when true and "0" when false. I've tried
>the following
>
>@myTrue = true
>def @myTrue.to_s
>	return "1"
>end
>
>however creating an anonymous class doesn't seem to be allowed and
>this affected the results of the original true instance (it now
>returns "1" as well) which I'd prefer stayed untouched.
>
>I thought of using numbers such as 1 for true but 0 is not false in a
>boolean expression.
>
>So is there a way to create an object that acts like a true or false
>when in boolean expression but still be modified without changing the
>true or false global objects? Or is there any function called in the
>evaluation of boolean expresssions which would allow me to ducktype a
>modified object?
>

You say you want to have it return a string "1", but what if you return 
an Integer 1 instead?  TrueClass doesn't have a to_i method defined in 
it, so you could do:

class TrueClass
  def to_i
    return 1
  end
end

Alternatively, TrueClass doesn't have a to_str method defined either, so 
if you _really_ need a string you could define:

class TrueClass
  def to_str
    return "1"
  end
end

....but of course, if you're looking to use this in places where to_s is 
automatically called (like in puts) then it won't work right.  


The problem is that 'true' and 'false' are treated as boolean literals, 
so whenever you use them you get a TrueClass or FalseClass.  I think that 
means that you can't just have a MyTrueClass that inherits from TrueClass 
and have it work right - it won't.  That means you have to define new 
methods on TrueClass/FalseClass.

I think your best bet is to define the to_i method on TrueClass (as 
above) because that's really what you're trying to get, an integer.  Then 
if you need a string you can convert the resulting integer to a string 
explicitly.


Phil