From: Robert Klemme <bob.news@...>
Date: 2005-11-09T07:42:12+09:00
Subject: Re: gsub and gsub! are inconsistent

aurelianito <aurelianocalvo@yahoo.com.ar> wrote:
> Hi all!
>
> I've been trying to optimize the code
> a_string.gsub(/pattern_1/, "REPLACE_1").gsub(/pattern_2/,
> "REPLACE_2").gsub(/PATTERN_3/,"REPLACE_3").
>
> with a_string.gsub(/pattern_1/, "REPLACE_1").gsub!(/pattern_2/,
> "REPLACE_2").gsub!(/pattern_3/,"REPLACE_3") (note the '!' on the
> second and third gsub).
>
> IMHO, this two blocks of pseudocode should behave in the same way, but
> if the second pattern don't matches, it returns null on the second
> version, and then generates an exception.
> Why is it than the destructive gsub behaves differently?

To be able to determine whether something was changed

if s.gsub!(...)
  puts "oops, changed!"
end

> Do you think that the current behaviour is the right behaviour? Why?

If there were no other reasons then at least existing code.  But there are 
other reasons (see above).

Btw, did you consider changing your code altoghether?  Depending on your 
patterns and replacements, there are other options possible:

s.gsub!(/pat1|pat2/) {|m|  replacements[m]}

s.gsub! /(pat1)|(pat2)/ do |m|
  case
    when m[1]; "re1"
    when m[2]; "re2"
    else raise "Unexpected"
  end
end

Kind regards

    robert