From: Steven D'Aprano <steve@...>
Date: 2007-10-25T10:45:02+09:00
Subject: Intervals in Ruby

Howdy,

I'm not a Ruby developer *at all*, I use Python, but this is not flame-
bait. I'm interested in how Ruby folks find using intervals.

In Python, we deal with integer ranges virtually exclusively with the 
range() function. range() always results in a half-open interval:

range(5) => 0, 1, 2, 3, 4
range(1, 5) => 1, 2, 3, 4
range(4, -1, -1) => 4, 3, 2, 1, 0

The start argument is always included, the end argument is never 
included, and there is an optional step size (defaults to 1).


I understand that in Ruby you have quite a few choices, some of which are 
half-open like Python, some of which are closed:

0..5 => 0, 1, 2, 3, 4, 5
0...5 => 0, 1, 2, 3, 4

5.downto(1) => 5, 4, 3, 2, 1
1.upto(5) => 1, 2, 3, 4, 5
5.times() => 0, 1, 2, 3, 4
5.step(11, 3) => 5, 8, 11

and the Range.new method.

My question is: how useful are all these different mechanisms? Do you 
find that having two operators .. and ... is a blessing, or a curse 
because you can never remember which is which?

How useful are the closed interval forms? Do you find yourself making off-
by-one errors or needing to increment/decrement variables by one?

e.g. do you often need to write things like:

start.step(end + 1, increment){| i | block }
start.step(end - 1, increment){| i | block }

Writing in Python, I almost never need to "shift the fence-posts", so to 
speak. E.g. I virtually never need to write something like:

range(start, end+1)

to avoid an off-by-one error. When I used to program in Pascal (which 
exclusively uses closed intervals) I used to need to do it all the time. 
What's the Ruby experience?



Thank you,




-- 
Steven