From: Rick DeNatale <rick.denatale@...>
Date: 2007-09-23T04:24:46+09:00
Subject: Re: Idiomatic Ruby for Array#extract / Range#length?

On 9/22/07, Olivier Renaud <o.renaud@laposte.net> wrote:
> Le jeudi 20 septembre 2007 14:28, Sammy Larbi a �crit:
> > During the monthly meeting of our code dojo, we were surprised by a couple
> > of things in Ruby, so I had a couple of questions I'd like to ask the
> > community:
> >
> > 1) Would it make sense to talk about a Range having a length, as in:
> >
> > class Range
> >       def length
> >            self.end - self.begin
> >       end
> > end
>
> This code will work only when begin and end respond to #-. This is a valid
> implementation for Numeric objects, but not for other classes.
> In the general case, you'd have to generate every objects of the range to
> count them (using #to_a and #size).

I think that it's debatable even in the case of Numerics, for example:

(1.2..1.5).length #=> 0.3

Normally length returns the number of elements in a collection,  and
the method as provided doesn't actually work correctly for integer
ranges, it should be:

class Range
  def length
      1 + last - first
  end
end

But, what about:

(1...3).length

end-start would give 2 but:

(1...3).to_a => [1, 2]

To fix this:

class Range
   def length
       last - first + (exclude_end? ? 0 : 1)
  end
end

Now we have another case:

(3..1).to_a #=> []

so:

class Range
   def length
      [0, last - first + (exclude_end? ? 0 : 1)].max
  end
end

But then what about:

(1.2..1.5).length

A collection can't have 0.3 elements!

I think it only makes sense for Integer ranges.

-- 
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/