From: Florian Gross <flgr@...>
Date: 2004-09-06T04:50:12+09:00
Subject: Re: Style Question

Robert Klemme wrote:

>> Hello everybody,

Moin!

>> PS: How is for implemented? Can I maybe teach Number.downto to return an
>> object that
>>    is used by for to iterate like an inverse range?
> Even more straightforward: you can implement a range that supports both 
> directions yourself plus arbitrary stepping like this:

I'd prefer using an enumerator around Range#step or Fixnum#step instead.

Here are a few small comments and suggestion about your code. Maybe they 
are useful.

> class Rg
>  include Enumerable
> 
>  def initialize(from, to, step = sign(to - from))

What about String Ranges?

>    raise ArgumentError, "Invalid step #{step}" if (to - from) * step <= 0
>    @from, @to, @step = from, to, step
>    @to += @step - ((@to - @from) % @step)
>  end
> 
>  def each
>    x = @from
>    until x == @to

This is a problem -- there are Ranges that will never satisfy this 
condition. (Float ranges come to mind)

>      yield x
>      x += @step
>    end
>    self
>  end
> 
>  def sign(x)
>    case
>      when x > 0
>        1
>      when x == 0
>        0
>      else
>        -1
>    end
>  end

def sign(x); x <=> 0; end

> end

> Kind regards
>    robert

More regards,
Florian Gross