From: "Michael W. Ryder" <_mwryder@...>
Date: 2007-07-22T12:45:00+09:00
Subject: Re: Is there a replacement for sub?

Bernard Kenik wrote:
> ruby-talk-admin@ruby-lang.org wrote:
>>
>>
>>
>> ------------------------------------------------------------------------
>>
>> Subject:
>> Re: Is there a replacement for sub?
>> From:
>> "Robert Dober" <robert.dober@gmail.com>
>> Date:
>> Fri, 20 Jul 2007 20:49:07 +0900
>> To:
>> ruby-talk@ruby-lang.org (ruby-talk ML)
>>
>> To:
>> ruby-talk@ruby-lang.org (ruby-talk ML)
>>
>>
>> On 7/20/07, Martin DeMello <martindemello@gmail.com> wrote:
>>> On 7/20/07, Robert Dober <robert.dober@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]
> 
>