about_variable_scope.rb

require File.expand_path(File.dirname(__FILE__) + '/neo')

class AboutVariableScope < Neo::Koan

  def bark
    noise = "RUFF"
  end

  def test_noise_is_not_available_in_the_current_scope

    assert_raise(___) do
      noise
    end

  end

  def test_we_can_get_noise_by_calling_method
    assert_equal __, bark
  end

  inaccessible = "Outside our universe"
  def test_defs_cannot_access_variables_outside_scope
    # defined? does not return true or false
    assert_equal __, defined? inaccesible
  end

  # ------------------------------------------------------

  def test_blocks_can_access_variables_outside_scope 
    test = "Hi"
    (1..2).each do
      test = "Hey"
    end

    assert_equal __, test    
  end

  def test_block_variables_cannot_be_accessed_outside_scope
    (1..2).each do
      x = 0 
    end
    assert_equal __, defined? x
  end

  # ------------------------------------------------------

  class Mouse
    @@total = 0
    # Class variables are prefixed with two '@' characters.

    def initialize(n)
      @name = n
      # Instance variables are prefixed with one '@' character.
      @@total += 1 
    end

    def name
      @name
    end

    def Mouse.count
      @@total
    end
  end

  def test_instance_variable 
    oscar = Mouse.new("Oscar")
    assert_equal __, oscar.name 
  end

  def test_class_variable
    (1..9).each { |i| Mouse.new("#{i}") }
    # Things may appear easier than they actually are.  
    assert_equal __, Mouse.count
  end

  # Meditate on the following: 
  # What is the difference between a class variable and instance variable?

  # ------------------------------------------------------
  
  $anywhere = "Anywhere"
  # Global variables are prefixed with the '$' character.

  def test_global_variables_can_be_accessed_from_any_scope
    assert_equal __, $anywhere    
  end

  def test_global_variables_can_be_changed_from_any_scope
    # From within a method
    $anywhere = "Here"
    assert_equal __, $anywhere
  end

  def test_global_variables_retain_value_from_last_change
    # What is $anywhere?
    assert_equal __, $anywhere
  end

  def test_global_variables_can_be_changed_from_any_scope_2
    # From within a block
    (1..2).each do
      $anywhere = "Hey"
    end

    assert_equal __, $anywhere
  end

end

# THINK ABOUT IT:
# 
# What will $anywhere be down here, outside of the scope of the
# AboutVariableScope class?