Sugar-Free Ruby: An Experiment in Object-first Teaching

teaching_ruby_objects_first.rb

# http://www.confreaks.com/videos/1112-gogaruco2012-sugar-free-ruby-an-experiment-in-object-first-teaching
# https://github.com/simeonwillbanks/gogaruco2012/blob/master/02_Sugar-Free_Ruby:_An_Experiment_in_Object-first_Teaching.md


# Everything is an Object.

5 # => 5
42.0 # => 42.0
"Hello!" # => Hello!
[1, 2, 3] # => [1, 2, 3]


# Objects receive messages.

"six".send :upcase # =>SIX
5.send :+, 9 # => 14
17.send :nil? # => false


# Objects have a Class.

5.send :class # => Fixnum
4.0.send :class # => Float
["he's", "crazy"].send :class # => Array


# Teaching Objects
#
# The pen and the scribe.

# 1. Create a new Object and give it a name.
pen = Object.new
# => #<Object:0x007faae3882238>

# 2. Define a method. Methods respond to messages.
# Give the pen a nicer name than above.
def pen.to_s
  "A trusty pen"
end

pen.send :to_s
# => A trusty pen

# 3. A Pinch of sugar.
pen.to_s
# => A trusty pen

# 4. Errors are your friend.
# They tell you what to do next.
pen.write "Hi there"
# => NoMethodError: undefined method `write' for #<Object:A trusty pen>

# 5. Define the missing method
# Write all the things.
def pen.write thing
  Kernel.puts thing
end

pen.write "Hi"
# => Hi

pen.write pen
# => A trusty pen

# 6. Feature Request: Color
# We want the pen to contain an ink color.
pen.ink_color = "Blue"
# => NoMethodError: undefined method `ink_color=' for #<Object:A trusty pen>

# 7. Use an instance variable to save the ink color.
def pen.ink_color= color
  @ink_color = color
end

# 8. Show our colors.
# Redefine the to_s method to show the pen's color.
def pen.to_s
  "A trusty #{@ink_color} pen"
end

pen.ink_color = "purple"

pen.to_s
# => A trusty purple pen

# 9. Make it fancy.
# Implicit Receivers:
#   If you don't specify the Object to send a message to
#   it sends the message to itself.
def pen.sparkly_write thing
  write "*;. #{thing} *;.*"
end

pen.sparkly_write pen
# => *;. A trusty purple pen *;.*

# 10. Conditionals
# Redefine write to show the ink color if it is set.
# http://ascii-table.com/ansi-escape-sequences.php
# 30	Black
# 31	Red
# 32	Green
# 33	Yellow
# 34	Blue
# 35	Magenta
# 36	Cyan
# 37	White
def pen.write thing
  if @ink_color.downcase == 'black'
    Kernel.puts "\033[0;30;40m#{thing}\033[m"
  elsif @ink_color.downcase == 'red'
    Kernel.puts "\033[0;31;40m#{thing}\033[m"
  elsif @ink_color.downcase == 'green'
    Kernel.puts "\033[0;32;40m#{thing}\033[m"
  elsif @ink_color.downcase == 'yellow'
    Kernel.puts "\033[0;33;40m#{thing}\033[m"
  elsif @ink_color.downcase == 'blue'
    Kernel.puts "\033[0;34;40m#{thing}\033[m"
  elsif @ink_color.downcase == 'purple'
    Kernel.puts "\033[0;35;40m#{thing}\033[m"
  else
    Kernel.puts thing
  end
end

pen.write "I see #{pen.ink_color}"
# => I see purple

# 11. Define a Class.
# Class is a class that creates new classes.
Scribe = Class.new do
  def initialize pen
    @pen = pen
    @items = Array.new
  end

  def note item
    @items.push item
  end

  def write_everything
    @items.each do |item|
      @pen.write item
    end
  end
end

# 12. Puttig the Scribe to work.
fred = Scribe.new pen
# => #<Scribe:0x007f9df1a943e0 @items=[], @pen=#<Object:0x007f9df9a84730 @ink_color="green">>

fred.note "Time: #{Time.now}"
fred.note "Programming is awesome!"

fred.write_everything
# => Time: 2014-04-30 00:18:39 -0700
# => Programming is awesome!