自由に n 進数作る

custom_base_num.rb

#!/usr/bin/env ruby
# -*- coding: utf-8 -*-

class CustomBaseNum
  def self.convert(value, base_str)
    base = base_str.size
    result = ''
    while true
      break if value <= 0
      remainder = value % base
      value /= base
      result.insert 0, base_str[remainder]
    end
    result
  end
end

class Bignum
  alias :original_to_s :to_s
  def to_s(arg)
    if arg.is_a? String
      CustomBaseNum.convert self, arg
    else
      original_to_s arg
    end
  end
end

class Fixnum
  alias :original_to_s :to_s
  def to_s(arg)
    if arg.is_a? String
      CustomBaseNum.convert self, arg
    else
      original_to_s arg
    end
  end
end

p 10000000.to_s('01')
p 10000000.to_s(2)

p 10000000.to_s('0123456789')
p 10000000.to_s(10)

p 10000000.to_s('0123456789abcdef')
p 10000000.to_s(16)

p 10000000.to_s('0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ')
p 100000000000000000000000000000.to_s('0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ')