bbiker wrote: > On Jul 22, 10:39 pm, "Michael W. Ryder" <_mwry... / worldnet.att.net> > wrote: >> dbl... / wobblini.net wrote: >>> Hi -- >>> On Sun, 22 Jul 2007, 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 >>>> 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. >>>> 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] >>> I would very, very strongly advise you, and everyone else, not to do >>> this. You will break any code (inside the standard library and/or any >>> other code you load, or any code that uses your code) that depends on >>> the documented behavior of these methods. You may not like how sub! >>> and friends work, but it's a very bad idea to make the decision to >>> change them on behalf of everyone else, over and above the language >>> documentation. >> What I planned to do was get rid of the alias and change the name of the >> new sub! method to something like subf! for just that reason. I still >> prefer this version much better than the original version as there are >> no surprises. It is very hard to change 30+ years of practice overnight. >> >> >> >>> David- Hide quoted text - >> - Show quoted text -- Hide quoted text - >> >> - Show quoted text - > > Actually you do not have to define subf! as an intermediate step > you can directly define subn and subn! directly > > class String > def subn!(pattern, replacement, n = 1) > n.times { self.sub!(pattern, replacement) } > self # or return self > end > > def subn(pattern, replacement, n = 1) > return self if n < 1 > @str = self.sub(pattern, replacement) > (n-1).times { @str = @str.sub(pattern, replacement) } > @str # or return @str > end > end > > Note that sub and sub! are the original definitions > > You use subn(pattern, replacement) and subn!(pattern, replacement) as > substitutes for sub(pattern, replacement) and sub!(pattern, > replacement) which eliminate the unpleasant surprises. > > In addition, both can be safely chained !!!! > > Hope this helps > Thanks for the updated code. I think I will keep the subf and subf! definitions for when I want to do single replacements that are free of surprises. Maybe I will someday be able to use the original definitions with confidence but when I am in the middle of a programming run I hate to stop and look up language definitions to avoid problems. It just ruins the flow of thought.