小試身手

#!/usr/local/bin/ruby -w

class Fib

private

  def initialize  # constructor
    @fib_array = Array.new  # constructs an empty Array
    @fib_array[0] = 0
      # variables prefixed with an '@' are instance variables
    @fib_array[1] = 1
  end

  @@singleton = nil
    # variables prefixed with two '@'s are class variables

public

  def [] (n)  # operator overloading --- read-only
    while @fib_array.length <= n
      @fib_array.push(@fib_array[-1] + @fib_array[-2])
        # Array supports operations of a stack
    end
    @fib_array[n]
      # the last expression is what the function returns
  end

  def Fib.theFib
    # a class method --- prefixed with the class name and a dot (.)
    @@singleton = Fib.new if not @@singleton  # nil is false
    @@singleton
  end

end

(1..20).each {|i| puts Fib.theFib[i]}
# each is analogous to for_each algorithm in C++
# confusingly, in Ruby it's called an "iterator"
# {|i| puts Fib.theFib[i]} is analogous to a function object in C++
# in Ruby it's called a "block"

# output:
# 1
# 1
# 2
# 3
# 5
# 8
# 13
# 21
# 34
# 55
# 89
# 144
# 233
# 377
# 610
# 987
# 1597
# 2584
# 4181
# 6765

puts Fib.theFib[200]  # built-in support for big numbers

# output:
# 280571172992510140037611932413038677189525

除了大數，用標準 C++ 寫是也不會複雜到哪裡去啦。一口氣開始學兩種新語言，才體認 vi 之神妙 ─ Ruby 和 Common Lisp 竟然都認識 XD。