From: bbiker <renard3411@...>
Date: 2007-07-22T16:35:06+09:00
Subject: Re: Is there a replacement for sub?

On Jul 21, 11:40 pm, "Michael W. Ryder" <_mwry...@worldnet.att.net>
wrote:
> Bernard Kenik wrote:
> > ruby-talk-ad...@ruby-lang.org wrote:
>
> >> ------------------------------------------------------------------------
>
> >> Subject:
> >> Re: Is there a replacement for sub?
> >> From:
> >> "Robert Dober" <robert.do...@gmail.com>
> >> Date:
> >> Fri, 20 Jul 2007 20:49:07 +0900
> >> To:
> >> ruby-t...@ruby-lang.org (ruby-talk ML)
>
> >> To:
> >> ruby-t...@ruby-lang.org (ruby-talk ML)
>
> >> On 7/20/07, Martin DeMello <martindeme...@gmail.com> wrote:
> >>> On 7/20/07, Robert Dober <robert.do...@gmail.com> wrote:
>
> >>> > I was reading this whole thread and I kind of think to be dreaming, I
> >>> > must have missed something obvious!!!
> >>> > Anyway maybe this is was OP wants, well I think it is ;)
>
> >>> > 529/29 > irb
> >>> > irb(main):001:0> a='a b c d e f'
> >>> > => "a b c d e f"
> >>> > irb(main):002:0> a.gsub!(" ","")
>
> >>> Nope, he wants a method that only replaces the first n occurrences of
> >>> the pattern. gsub will not do this - you need to run sub in a loop.
> >>> (This is where perl's "continue matching where you left off" would
> >>> have been a nice optimisation)
>
> > The primary problem is that sub! returns nil when no substitutions are
> > made.
>
> > I have similar problem with Array#flatten!, Array#uniq! since it causes
> > problem when chaining!
> > My solution has been to override these bang! methods to return self even
> > when the bang! method did not have to change the receiver.
>
> > for sub! I would override the sub! method as follow
>
> > class String
> >  alias old_sub!  sub!
> >  def sub!(pattern, replacement)
> >      self.old_sub!(pattern, replacement)
> >      self
> >  end
> > end
>
> And this can easily be expanded to do what I was trying to do in the
> first place!  Adding the following method with your replacement method:
>
> class String
>    def subn!(pattern, replacement, n=1)
>      n.times do
>        self.sub!(pattern, replacement)
>      end
>    end
> end
>
> With this I can specify a.subn!(' ', '', 10) and it will return 'abcdef'
> just like I was looking for.  It will work with zero or negative values
> returning 'a b c d e f', again like I would expect.  Of course if you
> enter a non-integer value it will error out in its current state but the
> error is from the times method.
>
> > As a user of a method, I really do not care if the method did not have
> > to do anything so long as the object is in the desired state.
>
> I too hate surprises.
>
>
>
> > For an array such as  arr = [1,2,3,4,5,6], I can safely chain the bang!
> > methods without worrying about nil returns from flatten! and uniq!
>
> > arr.flatten!.uniq!.sort!    # NO ERROR MSG "undefined method `uniq!' for
> > nil:NilClass (NoMethodError)" because flatten! would have returned nil
> > p arr  =>  [1, 2, 3, 4, 5, 6]- Hide quoted text -
>
> - Show quoted text -- Hide quoted text -
>
> - Show quoted text -

Note that as written, subn! returns n. So if you need to do some
chaining, you should change subn! as follows:

   def subn!(pattern, replacement, n=1)
     n.times { self.sub!(pattern, replacement) }
     self
   end

str = "a b c d e f g h i j"
str.subn!(/ /,'',2).reverse!  # won't produce an error msg such as

C:/Documents ... /rb5C.tmp:30: undefined method `reverse!' for
1:Fixnum (NoMethodError)

instead of  => "j i h g f e d cba"