From: Logan Capaldo <logancapaldo@...>
Date: 2007-10-10T01:01:10+09:00
Subject: Re: Make a class evaluate to false in boolean expressions

On 10/9/07, Matt Margolis <matt@mattmargolis.net> wrote:
> I want to have a class that always evaluates to false in boolean
> expressions.  Is there a way to extend Ruby so that it evaluates an
> object of a class to false like false and nil?
>
> Example
>
> class AlwaysFalse
> end
>
> should_be_false = AlwaysFalse.new
>
> if should_be_false
>   #I don't want this to ever run
> else
>   #will always run
> end
>
> The use case for this is to have the concept of false but have it
> contain instance variables.  You can't stick instance variables on
> FalseClass because it is a singleton and every use of false will
> overwrite the previous instance variable values.
> a = false
> a.name = "fish"
> b = false
> b.name = "ocean"
> #at this point in time a.name is equal to "ocean" and not "fish" like I
> want.
>
> This example may seem like an awful design decision but in the program I
> am writing it is important to have an interface like this to meet the
> requirements I have to code against.
>
> Is achieving this behavior as simple as redefining some operator methods
> like == or is this sort of behavior not possible in Ruby?
>
The latter.

OTOH:

class Object
  def false?
    false
  end
end

class FalseClass
  def false?
     true
  end
end

class YourClass
   def false?
      true
   end
end

if condition.false?
 ...
end

Kind of annoying if you forget the .false? though. A better thing to
do would be to figure out what you are trying to model by having
multiple "falsy" values with some state.

> Thank you,
> Matt Margolis
>
>