From: Morton Goldberg <m_goldberg@...>
Date: 2007-10-28T08:30:30+09:00
Subject: Re: Truth value evaluating of an object

On Oct 27, 2007, at 10:35 AM, Dave River wrote:

> I know ruby treat an object as false whenever it is nil or false.
> However, I wonder if there are any other ways to change this behavior.
>
> For example, I define a class called AreYouOk.
> class AreYouOk
>       def initialize(ok)
>             @ok = ok
>       end
> end
>
> x = AreYouOk.new(false)
> puts "you are ok" if x
>
> Since x is not nil, ruby prints " you are ok".
> However, I want ruby to make the decision based on the @ok instance
> variable. Are there any ways to do that?
>
> I know that there is a method called __bool__ in Python. You can  
> define
> your __bool__ method in your class. The truth value of an object is
> based on the return value of __bool__. Does ruby provide similar
> mechanism?

What you are asking about looks to me like a flag class.

<code>
class Flag
    def initialize(state=false)
       @state = state
    end
    def set?
       @state
    end
    def set
       @state = true
    end
    def clear
       @state = false
    end
end

ok = Flag.new
puts "you are ok" if ok.set?
puts "you are not ok" unless ok.set?
ok.set
puts "you are ok" if ok.set?
puts "you are not ok" unless ok.set?

</code>

First the string "you are not ok" is printed. After the flag is set,  
the string "you are ok" is printed.

Regards, Morton