Splice random characters into a string

splice_rand_chars.rb

# builds an array of lower/upper case alphabet characters
# and returns a random character from that
def rand_char
  chars = (('a'..'z').to_a + 
           ('A'..'Z').to_a + 
           (0..9).to_a )
  chars[rand(chars.length)].to_s
end

# Takes a string str and returns it with random characters
# from rand_char spliced into every other character
def splice_rand_chars(str)
  index = 0
  until index >= str.length do
    str[index] += rand_char
    index += 2
  end
  str
end

puts splice_rand_chars("SPLICED")