no-ifs-commands-processor.rb

# response to http://jumpstartlab.com/news/archives/2013/04/23/the-death-of-ifs

#-----------------
# Commands :
#-----------------

class Command
  class Quit       ; def execute ; exit                   end end
  class Invalid    ; def execute ; puts 'invalid command' end end
  class Tweeting   ; def execute ; puts "tweeting"        end end
  class Retweeting ; def execute ; puts "retweeting"      end end
  class Commenting ; def execute ; puts "commenting"      end end
end

#----------------------------------
# Mapping : input -> 1 Command
#----------------------------------

class Commands
  MAPPING = Hash.new{ Command::Invalid.new }

  def self.register(input, command)
    MAPPING[input] = command
  end

  def self.command_for(input)
    MAPPING[input]
  end

  def self.valid_inputs
    MAPPING.keys
  end
end

Commands.register 'q', Command::Quit.new
Commands.register 't', Command::Tweeting.new
Commands.register 'r', Command::Retweeting.new
Commands.register 'c', Command::Commenting.new


#----------------------------------
# main loop
#----------------------------------
def show_prompt
  puts "Enter a command (one of #{Commands.valid_inputs.join(', ')})" ; true
end

while show_prompt && command = Commands.command_for(STDIN.gets.chomp)
  command.execute
end

tests.rb

#----------------------------------
# test input -> command mapping
#----------------------------------

def assert(condition) raise unless condition end


assert Commands.command_for('q').is_a?(Command::Quit)
assert Commands.command_for('t').is_a?(Command::Tweeting)
assert Commands.command_for('r').is_a?(Command::Retweeting)
assert Commands.command_for('c').is_a?(Command::Commenting)

assert Commands.command_for('?').is_a?(Command::Invalid)
assert Commands.command_for(' ').is_a?(Command::Invalid)


#----------------------------------
# test individual commands effect
#----------------------------------

require 'stringio'
def assert_output_is(expected)
  $stdout = StringIO.new
  yield
  unless expected == (actual_result = $stdout.string.chomp)
    raise "incorrect output : \n\texpected : #{expected} \n\tfound   : #{actual_result}"
  end
ensure
  $stdout = STDOUT
end


assert_output_is("tweeting"       ) { Command::Tweeting  .new.execute }
assert_output_is("retweeting"     ) { Command::Retweeting.new.execute }
assert_output_is("commenting"     ) { Command::Commenting.new.execute }
assert_output_is("invalid command") { Command::Invalid   .new.execute }

begin
  Command::Quit.new.execute
rescue SystemExit
  system_exit_triggered = true
ensure
  raise "Quit didn't exit" unless system_exit_triggered
end

I like it.

Limpide. Merci Alain.