Replace 2 strings at the same time?

hello

how can I replace 2 strings in the same time? for example let's say I have string like this:

str1 = "AAAA BBBB CCCC DDDD"

i want to replace every "AAAA" with "CCCC" and every "CCCC" with "AAAA" but if i did:

str1.gsub("AAAA","CCCC") # CCCC BBBB CCCC DDDD

str1.gsub("CCCC","AAAA") # AAAA BBBB AAAA DDDD

what I want str1 to be "CCCC BBBB AAAA DDDD"

From stackoverflow

• General answer:
  Use a regex to match both AAAA and CCCC, then substitute each match with CCCC and AAAA respectively.

  edit to clear up the confusion

  str1.gsub(/(AAAA|CCCC)/) { $1 == 'AAAA' ? 'CCCC' : 'AAAA' }
  

  edit i thought of a more elegant way too :)

  str1.gsub(/((AAAA)|(CCCC))/) { $2 ? 'CCCC' : 'AAAA' }
  

  Barry Fandango : Agree, that feels like a much better solution than the other suggestions. I can't figure out what the regex would be though.

  Morendil : Just use the alternation operator: AAAA|CCCC

  Barry Fandango : Agreed Morendil, but what would the replace syntax look like? You'll need to put your finds into groups like: (AAAA)|(CCCC) And then do some kind of trickiness in the replace with \1 and \2.

  some : javascript: "AAAA BBBB CCCC DDDD".replace(/AAAA|CCCC/g,function(a){ return a==="AAAA" ? "CCCC" : "AAAA";});

  Marcus Downing : My previous negative comment has been deleted, now I see what you mean.

  bobince : As SO's resident anti-regex-overuse whinger, I endorse this approach :-)

• Is it an option for you to replace AAAA with something else first and then proceed?

  str1.gsub("AAAA","WXYZ") # WXYZ BBBB CCCC DDDD
  str1.gsub("CCCC","AAAA") # WXYZ BBBB AAAA DDDD
  str1.gsub("WXYZ","CCCC") # CCCC BBBB AAAA DDDD
  

  alexandrul : Just take care at choosing the temporary string to replace AAAA with, it should not exist in the original string.

  Calyth : Don't know why the -1 was there... Technically, regular expression (as a language) has no memory. i.e. the accept solution above shouldn't work. Alexandrul already pointed out the pitfall. regular expression as a tool can do what the accepted solution does...

• A solution (although something based around regex would be best) would be something along the lines of creating a replacement hash as such, which can be extended as needed. I just quickly put this together to demonstrate. I'm sure with a bit more love and care you can come up with something more elegant that works along the same lines as this implementation only works for strings with spaces.

  str1 = "AAAA BBBB CCCC DDDD"    
  replacements = { "AAAA" => "CCCC", "CCCC" => "AAAA", "XXXX" => "ZZZZ" } # etc...
  
  new_string = ""
  str1.split(" ").each do |s| 
      new_string += replacements[s] || s
      new_string += " "
  end
  
  puts new_string # CCCC BBBB AAAA DDDD