From: Rob Burrowes <rob@...>
Date: 2006-05-04T10:13:01+09:00
Subject: Re: Newbee Question on what if x === 2..5 does

--Apple-Mail-239-894250713
Content-Transfer-Encoding: 7bit
Content-Type: text/plain;
	charset=US-ASCII;
	delsp=yes;
	format=flowed

Hmmm, it works if I bracket the range. Why is that?

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

On 4/05/2006, at 1:00 PM, Rob Burrowes wrote:

> I mistyped that (left out an =), but the same result.
>
> 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 12:42 PM, Rob Burrowes wrote:
>
>> 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
>>
>>
>
> 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
>
>

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-239-894250713--