ruby-metaprogramming.rb

# --- BEGIN EXAMPLE 1 ---
class MyClass
end

# Terminal
my_object = MyClass.new
my_object.class
my_object.superclass
MyClass.class
MyClass.superclass
# --- END EXAMPLE 1 ---


# --- BEGIN EXAMPLE 2 ---
class Bacon
  def fry
    puts "I'm being fried!"
  end
end

# Terminal
b = Bacon.new
b.fry
# --- END EXAMPLE 2 ---


# --- BEGIN EXAMPLE 3 ---
class Food
  def bake
    puts "400 degrees is where it's at"
  end
end

class Bacon < Food
  def fry
    puts "I'm being fried!"
  end
end

# Terminal
b = Bacon.new
b.bake

Bacon.ancestors
# --- END EXAMPLE 3 ---


# --- BEGIN EXAMPLE 4 ---
class Book
  def contents
    self
  end
end

b = Book.new

# Terminal
b.contents == b
b == Book.new
b == Book
# --- END EXAMPLE 4 ---


# --- BEGIN EXAMPLE 5 ---
module LibraryItem
  def contents
    self
  end
end

class Book
  include LibraryItem
end

b = Book.new

# Terminal
b.contents == b
b == Book.new
b == Book
# --- END EXAMPLE 5 ---


# --- BEGIN EXAMPLE 6 ---
class Book
  def self.contents
    self
  end
end

b = Book.new

# Terminal
b.contents
Book.contents
Book.contents == Book
# --- END EXAMPLE 6 ---


# --- BEGIN EXAMPLE 7 ---
foo = Array.new

def foo.size
  "Hello World!"
end

# Terminal
foo.size
foo.class

bar = Array.new
bar.size
bar.class

foo.singleton_methods
foo.singleton_class

bar.singleton_methods
bar.singleton_class
# --- END EXAMPLE 7 ---


# --- BEGIN EXAMPLE 8 ---
foo = Array.new

class << foo
  def size
    puts "Hello World!"
  end

  def uniq
    puts "There can be only one"
  end
end

# Terminal
foo.size
foo.uniq
foo.class

bar = Array.new
bar.size
bar.uniq
bar.class

foo.singleton_methods
foo.singleton_class

bar.singleton_methods
bar.singleton_class
# --- END EXAMPLE 8 ---


# --- BEGIN EXAMPLE 9 ---
class Book
  class << self
    def table_of_contents
      puts "where to find a topic"
    end

    def index
      puts "index of all those cool new terms"
    end

    def copyright
      puts "copyrighted yo"
    end
  end
end

# Terminal
b = Book.new
b.copyright
Book.copyright
# --- END EXAMPLE 9 ---


# --- BEGIN EXAMPLE 10 --- 
class Food
  def bake
    puts "400 degrees is where it's at"
  end
end

class Bacon < Food
  def fry
    puts "I'm being fried!"
  end

  def method_missing(m, *args)
    puts "Fry + Enjoy. There is nothing else."
  end
end

# Terminal 
b = Bacon.new
b.cook
f = Food.new
f.cook
# --- END EXAMPLE 10 ---


# --- BEGIN EXAMPLE 11 ---
class Food
  def bake
    puts "400 degrees is where it's at"
  end
end

class Bacon < Food
  def fry
    puts "I'm being fried!"
  end

  def method_missing(m, *args)
    puts "No method: #{m}"
    puts "No use for args: #{args}"
    puts "Fry + Enjoy. There is nothing else."
  end
end

# Terminal
b = Bacon.new
b.cook(degrees: 400)
# --- END EXAMPLE 11 ---


# --- BEGIN EXAMPLE 12 --- 
class Food
  define_method(:ymm) { puts "Did you say bacon?" }
end

# Terminal 
f = Food.new
f.ymm
# --- END EXAMPLE 12 ---


# --- BEGIN EXAMPLE 13 ---
class Food
  def bake
    puts "400 degrees is where it's at"
  end
end

class Bacon < Food
  def fry
    puts "I'm being fried!"
  end
  
  def method_missing(m, *args)
    puts "No method: #{m}"
    puts "No use for args: #{args}"
    puts "Fry + Enjoy. There is nothing else."
  end
end

class Strawberry < Food
  ['bake', 'fry'].each do |method_name|
    define_method(method_name) do
      puts "Forget that! Strawberries are delish as is"
    end
  end
end

# Terminal
berry = Strawberry.new
b.fry
# --- END EXAMPLE 13 ---


# --- BEGIN EXAMPLE 14 ---
class Food
  def bake
    puts "400 degrees is where it's at"
  end

  5.times do |i|
    define_method("buy_#{i}") { puts "#{i} #{self.class} added to shopping list" }
  end
end

# Terminal 
b = Food.new
b.buy_1
# --- END EXAMPLE 14 ---


# --- BEGIN EXAMPLE 15 ---
# Terminal
bacon = “Bacon”
bacon.define_singleton_method(:ymm) { puts “more please!” }
bacon.methods
bacon.singleton_methods

jam = “Jam”
jam.methods
jam.singleton_methods
# --- END EXAMPLE 15 ---


# --- BEGIN EXAMPLE 16 ---
class Person
  def initialize(args)
    define_singleton_method(args[:name]) { puts "heyo" }
  end
end

# Terminal
p = Person.new(name: ‘jane’)
p.jane
# --- END EXAMPLE 16 ---