From: Rob Burrowes <rob@...>
Date: 2006-05-04T09:42:45+09:00
Subject: Re: Newbee Question on what if x === 2..5 does

--Apple-Mail-237-892431984
Content-Transfer-Encoding: 7bit
Content-Type: text/plain;
	charset=US-ASCII;
	delsp=yes;
	format=flowed

I get what you mean. It makes sense to have the === as a method of  
the range, not of x, but this produces no result at all.

rob1:~ rbur004$ ruby -e 'a = [1,2,3,4,5,6,7,8,9,10]; a.each { |x|  
print x, "->"; if (2...5 == x) then print x, " " end; print "\n"}'
1->
2->
3->
4->
5->
6->
7->
8->
9->
10->


On 4/05/2006, at 11:06 AM, Jacob Fugal wrote:

> On 5/3/06, Rob Burrowes <rob@cs.auckland.ac.nz> wrote:
>> I'm new to ruby and don't understand why the following code does what
>> is does. Can anyone enlighten me?
>>
>> ruby -e 'a = [1,2,3,4,5,6,7,8,9,10]; a.each { |x| if (x === 2..5 )
>> then print x, " " end}; puts '
>> 2 3 4 5 6 7 8 9 10
>>
>> I would have thought this would be the same as
>>
>> ruby -e 'a = [1,2,3,4,5,6,7,8,9,10]; a.each { |x| case x; when 2..5
>> then print x, " "; end}; puts '
>> 2 3 4 5
>
> Try switching x === 2..5 to 2..5 === x. The case equality operator
> (===) is not cummutative. The conditions of a case statement are
> evaluated using the when condition as the *receiver* of the case
> equality operator, not the argument. Ie.
>
>  case a
>  when b
>    ...
>  end
>
> is equivalent to:
>
>  if b === a
>    ...
>  end
>
>> I am also confused that
>>
>> ruby -e 'while gets; print  if /<div id=.*$/ .. /<\/body>/; end' <  
>> fred
>> <div id="eutpuhe">
>> UETHUEPUK
>> THEUTEUH
>> teuhepxn
>> thueonhoe
>> ononueuouh
>> </div>
>> </body>
>>
>> and a three . range test give the same output.
>>
>> ruby -e 'while gets; print  if /<div id=.*$/ ... /<\/body>/; end'  
>> < fred
>> <div id="eutpuhe">
>> UETHUEPUK
>> THEUTEUH
>> teuhepxn
>> thueonhoe
>> ononueuouh
>> </div>
>> </body>
>
> Sorry, can't help you there. I always have a hard time remembering
> what the difference between .. and ... are in that context. I stay
> away from it in favor of more descriptive flagging in a while loop.
> E.g.:
>
>  flag = false
>  while line = gets
>    flag = true if line =~ /<div id=.*$/
>    flag = false if line =~ /<\/body>/
>    print line if flag
>  end
>
> Jacob Fugal
>

Rob

Rob Burrowes                     Ph:   +64 (9) 3737 599 Extn 87972
Computing Services Manager        Fax: +64 (9) 3737 453
Computer Science Department    Mob:+64 (27) 4731 856
The University of Auckland
Rm 391, Level 3
38 Princes Street                http://www.cs.auckland.ac.nz/~rob
Private bag 92019                http://www.wikarekare.org
Auckland 1001                    http://www.burrowes.org



--Apple-Mail-237-892431984--