From: Robert Klemme <bob.news@...>
Date: 2004-09-06T04:55:15+09:00
Subject: Re: Style Question


"Florian Gross" <flgr@ccan.de> schrieb im Newsbeitrag 
news:2q18quFqav8gU1@uni-berlin.de...
> 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?

That was just meant as an example - implementing integer ranges.  I probably 
should have pointed that out more clearly.

>>    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)

Yep, the int check is missing.

>>      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

Very nice!  Then we don't need sign():

def initialize(from, to, step = ((to - from) <=> 0))

>> end
>
>> Kind regards
>>    robert
>
> More regards,
> Florian Gross

EMR (even more regards)

    robert