Iterating and Incrementing Strings in Ruby

The Ruby String class has several methods that let you produce successive strings—that is, strings that increment, starting at the rightmost character. You can increment strings with next and next!(orsuccandsucc!). I prefer to usenext. (The methods ending in!make in-place changes.) For example:

  "a".next [or] "a".succ # => "b"

Remember,nextincrements the rightmost character:

  "aa".next # => "ab"

It adds a character when it reaches a boundary, or adds a digit or decimal place when appropriate, as shown in these lines:

  "z".next # => "aa" # two a's after onez
  "zzzz".next # => "aaaaa" # five a's after four z's
  "999.0".next # => "999.1" # increment by .1
  "999".next # => "1000" # increment from 999 to 1000

We’re not just talking letters here, but any character, based on the character set in use (ASCII in these examples):

  " ".next # => "!"

Chain calls ofnexttogether—let’s try three:

  "0".next.next.next # => "3"

As you saw earlier,nextworks for numbers represented as strings as well:

  "2007".next # => "2008"

Or you can get it to work when numbers are not represented as strings, though the method will come from a different class, notString. For example:

  2008.next # => 2009

Instead of fromString, this call actually uses thenextmethod fromInteger. (TheDate,Generator,Integer, andString classes all havenext methods.)

You can even use a character code viachrwithnext:

  120.chr # => "x"
  120.chr.next # => "y"

Theuptomethod fromString, which uses a block, makes it easy to increment. For example, this call touptoprints the English alphabet:

  "a".upto("z") { |i| print i } # => abcdefghijklmnopqrstuvwxyz

You could also do this with aforloop and an inclusive range:

  for i in "a".."z"
    print i
  end

You decide what’s simpler. Theforloop takes only slightly more keystrokes (29 versus 31, including whitespace). But I likeupto.