From: noreply@...
Date: 2007-03-23T20:28:09+09:00
Subject: [ ruby-Bugs-9490 ] Date module, step method, infinite loop if +step+ is 0 should raise an exception?

Bugs item #9490, was opened at 2007-03-23 11:28
You can respond by visiting: 
http://rubyforge.org/tracker/?func=detail&atid=1698&aid=9490&group_id=426

Category: Standard Library
Group: 1.8.5
Status: Open
Resolution: None
Priority: 3
Submitted By: Colin Bartlett (colinb2)
Assigned to: Nobody (None)
Summary: Date module, step method, infinite loop if +step+ is 0 should raise an exception?

Initial Comment:
The Date step method goes into an infinite loop if +step+ is 0,
but the Integer step method raises an exception if +step+ is 0.

This seems inconsistent, and I prefer the Integer step behaviour,
but I can be convinced that it's a desirable inconsistency.

I'm using the standard Ruby Installer for Windows
Ruby Version 1.8.5, Installer Version 185-21
ruby --version  ->  ruby 1.8.5 (2006-08-25) [i386-mswin32]

code of the step method in Tadayoshi Funaba's Date module
  # Step the current date forward +step+ days at a
  # time (or backward, if +step+ is negative) until
  # we reach +limit+ (inclusive), yielding the resultant
  # date at each step.
def step(limit, step)  # :yield: date
  da = self
  op = [:-,:<=,:>=][step<=>0]
  while da.__send__(op, limit)
    yield da
    da += step
  end
  self
end


 # The following is code to show the different behaviour
 # of Integer step and Date step when +step+ is 0.

$\ = "  " ; $, = "  "  # helps print output legibly on single lines

puts "\n ** Integer step example: exception raised if step = 0"
500.step( 505, 2 )  { | nxt |  print nxt }  # ->  500  502  504
50.step( 45, -2 )  { | nxt |  print nxt }  # ->  50  48  46
begin
  5.step( 5, 0 )  { | nxt |  puts nxt }
rescue 
  puts ' * exception raised: message = ' + $!.message
end  # ->   * exception raised: message = step can't be 0

require 'date'
c = Date.new( 2008, 1, 31 )
puts "\n\n ** Date step example:" + 
          " no error if step = 0, but an infinite loop?"
c.step( c + 3, 2 )   { | nxt |  print nxt }
                   # ->  2008-01-31  2008-02-02
c.step( c - 3, -2 )  { | nxt |  print nxt }
                   # ->  2008-01-31  2008-01-29
puts
count = 0

c.step( c, 0 ) { | nxt |
                     puts count.to_s + ": " + nxt.to_s
                     count += 1
                     break if count > 10
                   }  # -> "infinite" loop of 2008-01-31 ?


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You can respond by visiting: 
http://rubyforge.org/tracker/?func=detail&atid=1698&aid=9490&group_id=426