From: Robert Klemme <bob.news@...>
Date: 2004-05-23T19:48:44+09:00
Subject: Re: Zero is true ... whoda thunk?


"Dan Janowski" <danj@3skel.com> schrieb im Newsbeitrag
news:AE82CDF1-AAE8-11D8-AC4D-00039357B54C@3skel.com...
> I found this problem thorny when trying to export true/false to a
> database that does not support booleans (only int). So I wrote a class
> that magically does the conversion coming and going. Other than that, I
> find nil a very useful value and nice to be separate from numbers.

That inspired me to this piece of code:


CONVERSIONS = {}

def convert(obj)
  cv = find_converter obj
  cv ? cv.call( obj ) : obj
end

def find_converter(obj)
  obj.class.ancestors.each do |cl|
    x = CONVERSIONS[cl]
    return x if x
  end

  nil
end

CONVERSIONS[1.class] = proc {|x| x != 0}

convert 1023

You could even extend this to handle different target contexts (sometimes
you want int -> bool, sometimes int -> float):

def convert(obj, target=nil)
  cv = find_converter obj, target
  cv ? cv.call( obj ) : obj
end

def find_converter(obj, target)
  if target
    obj.class.ancestors.each do |cl|
      x = CONVERSIONS[ [cl, target] ]
      return x if x
    end
  else
    obj.class.ancestors.each do |cl|
      x = CONVERSIONS[cl]
      return x if x
    end
  end

  nil
end

....

Regards

    robert