nabeatsu.rb

#
# Nabeatsu
#   returns "hoge" if given value is a multiple of 3, or contains '3' in it; otherwise just the value itself (in String).
# 
# Restriction of coding:
#   DO NOT use conditional branching syntax, such as "if", "unless", "case ... when".
#
module Nabeatsu
  class << self
    def say(n)
      methods = [:hoge, :say_by_containing3, :say_by_containing3]
      method = methods[n % 3]
      self.send(method, n)
    end

    def hoge(n)
      "hoge"
    end

    def just(n)
      n.to_s
    end

    def bool_to_int(true_or_false)
      { false => 0,
        true  => 1,
      }[true_or_false]
    end

    def say_by_containing3(n)
      methods = [:just, :hoge]
      method = methods[bool_to_int(split_digit(n).member?(3))]
      self.send(method, n)
    end

    def split_digit(n)
      methods = [:empty_array, :split_next]
      method = methods[bool_to_int(n > 0)]
      self.send(method, n)
    end

    def split_next(n)
      split_digit(n / 10) << n % 10
    end

    def empty_array(n)
      []
    end
  end
end

nabeatsu_spec.rb

require File.join(File.dirname(__FILE__), "nabeatsu")

describe Nabeatsu do
  subject { Nabeatsu.say(n) }
  describe ".say" do
    context "given 1" do
      let(:n) { 1 }
      it { should == "1" }
    end
    
    context "given 3" do
      let(:n) { 3 }
      it { should == "hoge" }
    end
    
    context "given 4" do
      let(:n) { 4 }
      it { should == "4" }
    end
    
    context "given 6" do
      let(:n) { 6 }
      it { should == "hoge" }
    end
    
    context "given 12" do
      let(:n) { 12 }
      it { should == "hoge" }
    end
    
    context "given 13" do
      let(:n) { 13 }
      it { should == "hoge" }
    end
    
    context "given 20" do
      let(:n) { 20 }
      it { should == "20" }
    end
  end
end