Adding initial metaprogramming koans

.gitignore

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+dist
+.project_env.rc
+.path_progress
+*.rbc
+.idea

src/about_binding.rb

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+require File.expand_path(File.dirname(__FILE__) + '/edgecase')
+
+class AboutBinding < EdgeCase::Koan
+
+  class Foo
+    def initialize
+      @ivar = 22
+    end
+
+    def bar(param)
+      lvar = 11
+      binding
+    end
+  end
+
+  def test_binding_binds_method_parameters
+    binding = Foo.new.bar(99)
+    assert_equal 99, eval("param", binding)
+  end
+
+  def test_binding_binds_local_vars
+    binding = Foo.new.bar(99)
+    assert_equal 11, eval("lvar", binding)
+  end
+
+  def test_binding_binds_instance_vars
+    binding = Foo.new.bar(99)
+    assert_equal 22, eval("@ivar", binding)
+  end
+
+  def test_binding_binds_blocks
+    binding = Foo.new.bar(99) { 33 }
+    assert_equal 33, eval("yield", binding)
+  end
+
+  def test_binding_binds_self
+    foo = Foo.new
+    binding = foo.bar(99)
+    assert_equal foo, eval("self", binding)
+  end
+
+  def n_times(n)
+    lambda {|value| n * value}
+  end
+
+  def test_lambda_binds_to_the_surrounding_context
+    two_times = n_times(2)
+    assert_equal 6, two_times.call(3)
+  end
+
+  def count_with_increment(start, inc)
+    lambda { start += inc}
+  end
+
+  def test_lambda_remembers_state_of_bound_variables
+    counter = count_with_increment(7, 3)
+    assert_equal 10, counter.call
+    assert_equal 13, counter.call
+    assert_equal 16, counter.call
+  end
+
+end

src/about_blocks.rb

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+require File.expand_path(File.dirname(__FILE__) + '/edgecase')
+
+class AboutBlocks < EdgeCase::Koan
+
+  def test_calling_a_lambda
+    l = lambda {|a| a + 1}
+    assert_equal 100, l.call(99)
+  end
+
+  def test_calling_a_proc
+    p = Proc.new {|a| a + 1}
+    assert_equal 100, p.call(99)
+  end
+
+  def convert(&block)
+    block
+  end
+
+  def test_block_is_proc
+    b = convert {|a| a + 1}
+    assert_equal Proc, b.class
+    assert_equal 100, b.call(99)
+  end
+
+  def test_proc_takes_fewer_or_more_arguments
+    p = Proc.new {|a, b, c| a.to_i + b.to_i + c.to_i}
+    assert_equal 3 , p.call(1,2)
+    assert_equal 6, p.call(1,2,3,4)
+  end
+
+  def test_lambda_does_not_take_fewer_or_more_arguments
+    l = lambda {|a, b, c| a.to_i + b.to_i + c.to_i}
+    assert_raises(ArgumentError) do
+      l.call(1, 2)
+    end
+
+    assert_raises(ArgumentError) do
+      l.call(1,2,3,4)
+    end
+  end
+
+  def method(lambda_or_proc)
+    lambda_or_proc.call
+    :from_method
+  end
+
+  def test_return_inside_lambda_returns_from_the_lambda
+    l = lambda { return :from_lambda }
+    result = method(l)
+    assert_equal :from_method, result
+  end
+
+  def test_return_inside_proc_returns_from_the_context
+    p = Proc.new { return :from_proc }
+    result = method(p)
+    # The execution never reaches this line because Proc returns
+    # outside the test method
+    assert_equal __, p.call
+  end
+end

src/about_class_as_constant.rb

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+require File.expand_path(File.dirname(__FILE__) + '/edgecase')
+
+class AboutClassAsConstant < EdgeCase::Koan
+
+  class Foo
+    def say_hello
+      "Hi"
+    end
+  end
+
+  def test_defined_tells_if_a_class_is_defined_or_not
+    assert_not_nil defined?(Foo)
+    assert_nil defined?(Bar)
+  end
+
+  def test_class_is_a_constant
+    assert_equal "constant", defined?(Foo)
+  end
+
+  def test_class_constant_can_be_assigned_to_var
+    my_class = Foo
+    assert_equal "Hi", my_class.new.say_hello
+  end
+
+  @@return_value_of_class =
+    class Baz
+      def say_hi
+        "Hello"
+      end
+      99
+    end
+
+  def test_class_definitions_are_active
+    assert_equal 99, @@return_value_of_class
+  end
+
+  @@self_inside_a_class =
+    class Baz
+      def say_hi
+        "Hi"
+      end
+      self
+    end
+
+  def test_self_inside_class_is_class_itself
+    assert_equal Baz, @@self_inside_a_class
+  end
+
+  def test_class_is_an_object_of_type_class_and_can_be_created_dynamically
+    cls = Class.new
+    assert_match  /Class/, cls.to_s
+  end
+end

src/about_class_inheritance.rb

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+require File.expand_path(File.dirname(__FILE__) + '/edgecase')
+
+class AboutClassInheritance < EdgeCase::Koan
+
+  def test_singleton_class_can_be_used_to_define_singleton_methods
+    animal = "cat"
+    class << animal
+      def speak
+        "miaow"
+      end
+    end
+    assert_equal "miaow", animal.speak
+  end
+
+  class Foo
+    class << self
+      def say_hello
+        "Hello"
+      end
+    end
+  end
+
+  def test_singleton_class_can_be_used_to_define_class_methods
+    assert_equal "Hello", Foo.say_hello
+  end
+
+end

src/about_class_methods.rb

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+require File.expand_path(File.dirname(__FILE__) + '/edgecase')
+
+class AboutClassMethods < EdgeCase::Koan
+
+  class Foo
+    def self.say_hello
+      "Hello"
+    end
+  end
+
+  def test_class_is_an_instance_of_class_Class
+    assert_equal true, Foo.class == Class
+  end
+
+  def test_class_methods_are_just_singleton_methods_on_the_class
+    assert_equal "Hello", Foo.say_hello
+  end
+
+  def test_classes_are_not_special_and_are_just_like_other_objects
+    assert_equal true, Foo.is_a?(Object)
+    assert_equal true, Foo.superclass == Object 
+  end
+end

src/about_define_method.rb

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+require File.expand_path(File.dirname(__FILE__) + '/edgecase')
+
+class AboutDefineMethod < EdgeCase::Koan
+
+  class Example
+    def start
+      def stop
+        :stopped
+      end
+      :started
+    end
+  end
+
+  def test_methods_can_define_other_methods
+    o = Example.new
+    assert_raises(NoMethodError) do
+      o.stop
+    end
+
+    o.start
+
+    assert_equal :stopped, o.stop
+  end
+
+  class Example
+    def foo
+      def foo
+        :new_value
+      end
+      :first_value
+    end
+  end
+
+  def test_methods_can_redefine_themselves
+    o = Example.new
+    assert_equal :first_value, o.foo
+    assert_equal :new_value, o.foo
+  end
+
+  class Multiplier
+    def self.create_multiplier(n)
+      define_method "times_#{n}" do |val|
+        val * n
+      end
+    end
+
+    10.times {|i| create_multiplier(i) }
+  end
+
+  def test_define_method_creates_methods_dynamically
+    m = Multiplier.new
+    assert_equal 30, m.times_3(10)
+    assert_equal 60, m.times_6(10)
+    assert_equal 90, m.times_9(10)
+  end
+
+  module Accessor
+    def my_writer(name)
+      ivar_name = "@#{name}"
+      define_method "#{name}=" do |value|
+        #Write code here to set value of ivar
+        instance_variable_set(ivar_name, value)
+      end
+    end
+
+    def my_reader(name)
+      ivar_name = "@#{name}"
+      define_method name do 
+        #Write code here to get value of ivar
+        instance_variable_get(ivar_name)
+      end
+    end
+  end
+
+  class Cat
+    extend Accessor
+    my_writer :name
+    my_reader :name
+  end
+
+  def test_instance_variable_set_and_instance_variable_get_can_be_used_to_access_ivars
+    cat = Cat.new
+    cat.name = 'Fred'
+    assert_equal 'Fred', cat.name
+  end
+end
+