metakoans_training/meta_koans.rb

#
# meta_koans.rb is an arduous set of exercises designed to stretch
# meta-programming muscle.  the focus is on a single method "attribute" which
# behaves much like the built-in "attr", but whose properties require delving
# deep into the depths of meta-ruby.  usage of the "attribute" method follows
# the general form of
#
#   class C
#     attribute "a"
#   end
#
#   o = C.new
#   o.a = 42  # setter - sets @a
#   o.a       # getter - gets @a
#   o.a?      # query - true if @a
#
# but reaches much farther than the standard "attr" method as you will see
# shortly.
#
# your path, should you choose to follow it, is to write a single file
# "knowledge.rb" implementing all functionality required by the koans below.
# as a student of meta-programming your course will be guided by a guru whose
# wisdom and pithy sayings will assist you on your journey.
#
# a successful student will eventually be able to do this
#
#   harp:~ > ruby meta_koans.rb
#   koan_1 has expanded your awareness
#   koan_2 has expanded your awareness
#   koan_3 has expanded your awareness
#   koan_4 has expanded your awareness
#   koan_5 has expanded your awareness
#   koan_6 has expanded your awareness
#   koan_7 has expanded your awareness
#   koan_8 has expanded your awareness
#   koan_9 has expanded your awareness
#   mountains are again merely mountains
#
require_relative "meta_guru"
require_relative "meta_student"

# knowledge = ARGV.shift or abort "#{ $0 } knowledge.rb"
koan = ARGV[0]
rev = ARGV[1]
student = MetaStudent.new "knowledge/koan_0#{koan}_#{rev}"

module MetaKoans

  #
  # "attribute" must provide getter, setter, and query for "a" to instances of SomeClass
  #
  def koan_1
    SomeClass.attribute

    o = SomeClass.new

    assert{ not o.a? }
    assert{ o.a = 42 }
    assert{ o.a == 42 }
    assert{ o.a? }
  end

  #
  # the name of the getter, setter, and query methods created by "attribute" must match
  # the value of the given parameter
  #
  def koan_2
    SomeClass.attribute "b"

    o = SomeClass.new

    assert{ not o.b? }
    assert{ o.b = 41 }
    assert{ o.b == 41 }
    assert{ o.b? }
  end

  #
  # multiple calls to "attribute" with different parameter values must generate multiple
  # methods whose names correspond to the parameter value, and whose values must must be
  # independent of each other
  #
  # this koan also illustrates how calling "attribute" through SomeClass.class_eval
  # has the same effect as calling "attribute" directly on SomeClass.
  #
  # additionally, by virtue of the fact that "attribute" is available and working on
  # SomeClass, creating an attribute on an object-specific class should automatically
  # work
  #
  def koan_3
    SomeClass.attribute "c"

    o = SomeClass.new

    assert{ not o.c? }
    assert{ o.c = 39 }
    assert{ o.c == 39 }
    assert{ o.c? }

    SomeClass.class_eval { attribute "d" }

    assert{ not o.d? }
    assert{ o.d = 38 }
    assert{ o.d == 38 }
    assert{ o.d? }

    class << o
      attribute "e"
    end

    assert{ not o.e? }
    assert{ o.e = 37 }
    assert{ o.e == 37 }
    assert{ o.e? }
  end

  #
  # "attribute" must be callable from the singleton class of SomeClass, and must
  # generate corresponding getter, setter, and query methods on the class itself
  # in addition to instances of it.
  #
  def koan_4
    SomeClass.class_eval do
      class << self
        self.attribute "f"
        attribute "g"
      end
    end

    assert{ not SomeClass.f? }
    assert{ SomeClass.f = 36 }
    assert{ SomeClass.f == 36 }
    assert{ SomeClass.f? }

    assert{ not SomeClass.g? }
    assert{ SomeClass.g = 35 }
    assert{ SomeClass.g == 35 }
    assert{ SomeClass.g? }
  end

  #
  # "attribute" must provide a method for providing a default value as hash
  #
  def koan_5
    SomeClass.class_eval do
      attribute "h" => 34
      attribute "i" => 33
    end

    o = SomeClass.new

    assert{ o.h == 34 }
    assert{ o.h? }
    assert{ (o.h = nil).nil? }
    assert{ o.h == nil }
    assert{ not o.h? }

    assert{ o.i == 33 }
    assert{ o.i? }
    assert{ (o.i = nil).nil? }
    assert{ o.i == nil }
    assert{ not o.i? }
  end

  #
  # "attribute" must provide a method for providing a default value as block
  # which is evaluated at instance level
  #
  # instance_eval is called to define an attribute in order to illustrate the
  # difference between it and class_eval. this code should not affect your
  # mastery of this koan
  #
  def koan_6
    SomeClass.class_eval do
      attribute("j"){ thirtytwo }
      attribute("k"){ j - 1 }
      def thirtytwo
        32
      end
    end

    o = SomeClass.new

    assert{ o.j == 32 }
    assert{ o.j? }
    assert{ (o.j = nil).nil? }
    assert{ o.j == nil }
    assert{ not o.j? }

    o.j = 32
    assert{ o.k == 31 }
    assert{ o.k? }
    assert{ (o.k = nil).nil? }
    assert{ o.k == nil }
    assert{ not o.k? }

    SomeClass.instance_eval do
      class << self
        attribute("l"){ thirtyone }
      end
      def thirtyone
        31
      end
    end

    assert{ SomeClass.thirtyone == 31 }
    assert{ SomeClass.l == 31 }
    assert{ SomeClass.l? }
    assert{ (SomeClass.l = nil).nil? }
    assert{ SomeClass.l == nil }
    assert{ not SomeClass.l? }
  end

  #
  # "attribute" must be available to any class
  #
  def koan_7
    c = Class.new do
      class << self
        attribute "m"
      end
      attribute "n"
    end

    assert{ not c.m? }
    assert{ c.m = 30 }
    assert{ c.m == 30 }
    assert{ c.m? }

    o = c.new

    assert{ not o.n? }
    assert{ o.n = 29 }
    assert{ o.n == 29 }
    assert{ o.n? }
  end

  #
  # "attribute" must be available to any module
  #
  def koan_8
    m = Module.new do
      attribute "o"
    end

    c = Class.new do
      include m
      extend m
    end

    assert{ not c.o? }
    assert{ c.o = 28 }
    assert{ c.o == 28 }
    assert{ c.o? }

    o = c.new

    assert{ not o.o? }
    assert{ o.o = 27 }
    assert{ o.o == 27 }
    assert{ o.o? }
  end

  #
  # into the void
  #
  def koan_9
    b = Class.new {
      class << self
        attribute "a" => 48
        attribute("b"){ a + 1 }
      end
      include Module.new {
        attribute "a" => 50
        attribute("b"){ a + 1 }
      }
    }

    c = Class.new b

    assert{ c.a == 48 }
    assert{ c.a? }
    assert{ c.a = "forty-two" }
    assert{ c.a == "forty-two" }
    assert{ b.a == 48 }
    c.a = 48

    assert{ c.b == 49 }
    assert{ c.b? }
    assert{ c.b = "forty-two" }
    assert{ c.b == "forty-two" }
    assert{ b.b == 49 }

    o = c.new

    assert{ o.a == 50 }
    assert{ o.a? }
    assert{ o.a = nil; o.a == nil }
    assert{ not o.a? }
    o.a = 50

    assert{ o.b == 51 }
    assert{ o.b? }
    assert{ o.b = nil; o.b == nil }
    assert{ not o.b? }
  end

  def assert()
    bool = yield
    raise StandardError, "assert{ #{ caller.first[%r/^.*(?=:)/] } } #=> #{ bool.inspect }" unless bool
    bool
  end
end

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