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Replacing Multiple Patterns in a Single Pass
CodeExpectedActual
class String
  def mgsub(key_value_pairs=[].freeze)
    regexp_fragments = key_value_pairs.collect { |k,v| k }
    gsub(Regexp.union(*regexp_fragments)) do |match|
      key_value_pairs.detect{|k,v| k =~ match}[1]
    end	
  end
end
"GO HOME!".mgsub([[/.*GO/i, 'Home'], [/home/i, 'is where the heart is']])
 "Home is where the heart is!" "Home is where the heart is!" 
"Here is number #123".mgsub([[/[a-z]/i, '#'], [/#/, 'P']])
 "#### ## ###### P123" "#### ## ###### P123" 
"FOO bar".gsub(/foo/i, "The bar").gsub(/bar/m, "result")
 "The result result" "The result result" 
"Here is number #123".gsub(/[a-z]/i, "#").gsub(/#/, "P")
 "PPPP PP PPPPPP P123" "PPPP PP PPPPPP P123" 
"between".mgsub(/ee/ => 'AA', /e/ => 'E')        # Bad code
 "bEtwEEn" "bEtwEEn" 
"between".mgsub([[/ee/, 'AA'], [/e/, 'E']])      # Good code
 "bEtwAAn" "bEtwAAn"