metaprogramming-examples

gistfile1.txt

# refinements.rb
module TimeExtensions
  refine Integer do
    def minutes; self * 60.000001; end
  end
end

class MyApp
  using TimeExtensions

  def initialize
    p 2.minutes
  end
end

MyApp.new
p 3.minutes

gistfile2.txt

# method_binding.rb
class MyClass
  def initialize(value)
    @x = value
  end

  def my_method
    @x
  end
end

class MyClass2 < MyClass
end

object = MyClass.new(1)
m = object.method(:my_method)
m.call # => 1

unbound = m.unbind

another_object = MyClass2.new(2)
m = unbound.bind(another_object)
m.call

gistfile3.txt

# template_engine.rb
class Template
  def initialize(locals, &block)
    @template = ''
    @indent = 0

    m = Module.new do
      locals.each do |(k, v)|
        define_method(k) { v }
      end
    end

    extend(m)
    instance_eval(&block)
  end

  def text(string)
    @template += indent(string) + "\n"
  end

  def method_missing(name, attributes = {})
    attributes_string =
      attributes.reduce('') { |acc, (k, v)| acc + " #{k}=#{v}" }

    @template += indent("<#{name}#{attributes_string}>\n")
    @indent += 2
    yield
    @indent -= 2
    @template += indent("</#{name}>\n")
  end

  def indent(str)
    ' ' * @indent + str
  end

  def to_s
    @template
  end
end

records = 5.times.map do |i|
  Struct
    .new(:url, :title)
    .new("articles/#{i + 1}", "Article #{i + 1}")
end

template = Template.new(articles: records) do
  div class: 'wrapper', id: 'wrapper' do
    h1 class: 'title' do
      text 'Hello world'
    end

    ul do
      articles.each do |article|
        li do
          a href: article.url do
            text article.title
          end
        end
      end
    end
  end
end

puts template.to_s
File.write('index.html', template.to_s)

gistfile4.txt

# module-extensions.rb
module M
  module ClassMethods
    def find(str)
      'hello ' + str
    end
  end

  module InstanceMethods
    def age
      25
    end
  end

  def self.included(klass)
    klass.include InstanceMethods
    klass.extend ClassMethods
  end
end

class Person
  include M
end

puts Person.find('world')
puts Person.new.age