From: Wesley J Landaker <wjl@...>
Date: 2003-06-26T22:31:57+09:00
Subject: Re: String#split(' ') and whitespace (perl user's surprise)

On Thursday 26 June 2003 6:14 am, Mike Stok wrote:
> I have to confess that I use a lot of Perl, and some of its idioms
> are deeply embedded in my mind.
>
> Im the course of parsing some data in Ruby I used a fragment of code
> like
>
>     rules.each_line do |rule|
>       sku, price, special = rule.chomp.split(' ', 3)
>       # [...]
>     end
>
> where rules was composed of lines of the form
>
>       A     50       3 for 130
>
> coming from a perl background I would have expected 'A', '50' and '3
> for 130' to have been assigned to sku, price and special.  As it
> turned out special had leading whitespace.
>
> Maybe this is the difference Hal alludes to in From Perl to Ruby in
> his book The Ruby Way:  "Also, note that split also behaves slightly
> differently."
>
> Is this intentional behaviour?  I think that the Perl behaviour is
> more useful (that is trimming the leading whitespace off the limit-th
> element returned.)

I don't know if it's intentional or not, but I do see the following at 
http://www.rubycentral.com/book/ref_c_string.html#String.split

  split 
  str.split( pattern=$;, [ limit ] ) -> anArray 

  Divides str into substrings based on a delimiter, returning an array  
  of these substrings. 

  If pattern is a String, then its contents are used as the delimiter
  when splitting str. If pattern is a single space, str is split on
  whitespace, with leading whitespace and runs of contiguous whitespace
  characters ignored. 

And they have an example:

  " now's  the time".split(' ') 損 ["now's", "the", "time"]

This seems to imply that split(' ', 3) ought to work like you were 
expecting. A little testing with irb seems to show that this behaves 
differently any time the "limit" argument is given. In fact, when a 
regex matching whitespace is given, you get an extra empty entry at the 
front; this is another possible problem, but maybe is correct since 
it's not the "magic" single space parameter which is said to trim 
leading whitespace. See below:

$ cat test.rb
str = "       A     50       3 for 130"

p str.split
p str.split(' ')
p str.split(' ',3)
p str.split(/\s+/)
p str.split(/\s+/,3)

$ ./ruby -v test.rb
ruby 1.8.0 (2003-05-31) [i686-linux]
["A", "50", "3", "for", "130"]
["A", "50", "3", "for", "130"]
["A", "50", "      3 for 130"]  <-- this differs from what is documented
["", "A", "50", "3", "for", "130"]
["", "A", "50       3 for 130"]
 
This seems like a ruby bug: limit seems to be counting whitespace 
characters and not whitespace "runs" when ' ' is given as the pattern.

But maybe it's a documentation bug. Who knows?

-- 
Wesley J. Landaker - wjl@icecavern.net
OpenPGP FP: C99E DF40 54F6 B625 FD48  B509 A3DE 8D79 541F F830