An alternative to String#next/#succ for incrementing strings

gistfile1.txt

describe String do
  describe "#increment and #increment!" do
    it 'should increment nothing to 1' do
      "Something".increment.should == "Something1"
    end
    
    it 'should increment the digits in the string' do
      "789".increment.should == "790"
    end

    it 'should pay attention to spacing' do
      "Foo bar 3".increment.should == "Foo bar 4"
    end

    it 'should increment digits' do
      " whateverrrr 99".increment.should == " whateverrrr 100"
    end
    
    it 'should set the original value with bang' do
      x = " foobar 123"
      x.increment!
      x.should == " foobar 124"
    end
    
    it 'should follow the format if given' do
      " foobar ".increment("(%s)").should == " foobar (1)"
      " foobar (134)".increment("(%s)").should == " foobar (135)"
      " foobar(134) ".increment("(%s)").should == " foobar(134) (1)"
      " foobar [789]".increment.should == " foobar [789]1"
      " foobar [789]".increment("[%s]").should == " foobar [790]"
    end

    it 'should set the original value with bang' do
      x = " foobar (123)"
      x.increment!("(%s)")
      x.should == " foobar (124)"
    end
  end
end

class String
  # This is different from #next/#succ because it only increments digits.
  # Also, if it is incrementing from x-digits to y-digits, it will add the extra
  # digit instead of resetting to 0 and keeping x-digits.
  # 
  #   "abcd".increment      #=> "abcd1"
  #   "THX1138".increment   #=> "THX1139"
  #   "<<koala>>".increment #=> "<<koala>>1"
  #   "1999zzz".increment   #=> "1999zzz1"
  #   "ZZZ9999".increment   #=> "ZZZ10000"
  #   "***".increment       #=> "***1"
  #   "123".increment       #=> "124"
  #   " 123 ".increment     #=> " 123 1"
  #   " 123 ".increment     #=> " 123 1"
  #
  # You can pass in an optional format for the numbers where %s is the placeholder
  # for the digits:
  #
  #   " foobar (1)".increment #=> " foobar (2)"
  #   " foobar (789) ".increment #=> " foobar (789) (1)"
  #
  def increment(format=nil) 
    regexp = format ? Regexp.new(Regexp.escape(format).gsub('%s', '\d+')) : /\d/
    parts = format ? split(/(#{regexp})|(\D)/) : split(/(\D)/)
    num = (format || "%s") % 0
    parts.push(num) unless parts[-1] =~ regexp
    parts[-1] = if format 
                  parts[-1].sub(/(\d+)/) { |m| Integer(m) + 1  }
                else
                  Integer(parts[-1]) + 1
                end
    parts.join
  end
  
  def increment!(format=nil)
    replace(increment(format))
  end
end