$ gem install rack

class ShowEnv
  def call(env)
    [
      200,
      { 'Content-Type' => 'text/plain' },
      env.keys.sort.map { |k| "#{k} = #{env[k]}\n" }
    ]
  end
end

run ShowEnv.new

$ rackup

GATEWAY_INTERFACE = CGI/1.2
HTTP_ACCEPT = text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8
HTTP_ACCEPT_ENCODING = gzip, deflate, br
HTTP_ACCEPT_LANGUAGE = ko,ja;q=0.9,en-US;q=0.8,en;q=0.7
HTTP_CACHE_CONTROL = max-age=0
HTTP_CONNECTION = keep-alive
HTTP_HOST = localhost:9292
HTTP_SAVE_DATA = on
HTTP_UPGRADE_INSECURE_REQUESTS = 1
HTTP_USER_AGENT = Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/66.0.3359.45 Safari/537.36
HTTP_VERSION = HTTP/1.1
PATH_INFO = /
QUERY_STRING = 
REMOTE_ADDR = ::1
REQUEST_METHOD = GET
REQUEST_PATH = /
REQUEST_URI = /
SCRIPT_NAME = 
SERVER_NAME = localhost
SERVER_PORT = 9292
SERVER_PROTOCOL = HTTP/1.1
SERVER_SOFTWARE = puma 3.11.2 Love Song
puma.config = #<Puma::Configuration:0x007ff652a60680>
puma.socket = #<TCPSocket:0x007ff652a09cb8>
rack.after_reply = []
rack.errors = #<Rack::Lint::ErrorWrapper:0x007ff651039450>
rack.hijack = #<Proc:0x007ff6510396f8@/Users/jo/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/rack-2.0.4/lib/rack/lint.rb:525>
rack.hijack? = true
rack.input = #<Rack::Lint::InputWrapper:0x007ff651039478>
rack.multiprocess = false
rack.multithread = true
rack.run_once = false
rack.tempfiles = []
rack.url_scheme = http
rack.version = [1, 3]

class Foo
  def call(env)
    [200, {'Content-Type' => 'text/plain'}, ['Hello']]
  end
end

run Foo.new

class Foo       # module Foo も可
  def self.call(env)
    [200, {'Content-Type' => 'text/plain'}, ['Hello']]
  end
end

run Foo

run lambda {|env| [200, {'Content-Type' => 'text/plain'}, ['Hello']] }
# run proc {|env| ... } でも同じ

endpoint <-> middleware[s] ... <-> (Rack handler) <-> (server)

・・・

run Rails.application

Rack::Handler::WEBrick.run Foo.new, Port: 9292

Rack::Directory <-> Rack::Deflater <-> Rack::ETag <-> (Rack handler/server)

use Rack::ETag
use Rack::Deflater
run Rack::Directory.new 'public'

# useをrunに書き換えた場合
run Rack::ETag.new(
  Rack::Deflater.new(
    Rack::Directory.new 'public'
  )
)

use Rack::Static, urls: [''], root: 'public', index: 'test1.txt'

class Static

    def initialize(app, options={})
      @app = app
      @urls = options[:urls] || ["/favicon.ico"]

  ・・・

end

# 空のエンドポイント
class NullEndPoint
  def call(env)
  end
end

use Rack::ETag
use Rack::Deflater
use Rack::Static, urls: [''], root: 'public', index: 'test1.txt'
run NullEndPoint.new

require 'activerecord'
ActiveRecord::Base.establish_connection :adapter => "sqlite3",
                                        :database => "dbfile"

ActiveRecord::Base.connection.create_table :tasks do |t|
  t.string   :description
  t.boolean  :completed
end

class Task < ActiveRecord::Base; end

task = Task.new
task.description = 'ブログの記事作成'
task.completed = true
task.save
task.description # => "ブログの記事作成"
task.completed?  #=> true

task = Task.find(:first, :conditions => {:completed => true})
task.description # => "ブログの記事作成"

task = Task.find_by_description('ブログの記事作成')
task.id # => 1

Task.find_all_by_completed(true)
Task.find_by_description_and_completed('ブログの記事作成', true)
Task.find_or_create_by_description('ランチターイム')
Task.find_by_description!('帰宅')

module MixinSamples
  module StudentsData
    def self.included(base)
      base.extend self
    end

    def data
      [
        { age: 18, name: 'Suzuki', japanese: 70, math: 80, science: 90, english: 70 },
        { age: 17, name: 'Sato', japanese: 60, math: 70, science: 50, english: 50 },
        { age: 18, name: 'Takahashi', japanese: 90, math: 90, science: 100, english: 70 },
        { age: 16, name: 'Tanaka', japanese: 80, math: 60, science: 70, english: 90 }
      ]
    end
  end
end

module MixinSamples
  module TeachersData
    def self.included(base)
      base.extend self
    end

    def data
      [
        { age: 46, name: 'Ito', teaching_subject: '国語', teaching_target: '1年生' },
        { age: 38, name: 'Watanabe', teaching_subject: '数学', teaching_target: '2年生' },
        { age: 25, name: 'Yamamoto', teaching_subject: '科学', teaching_target: '3年生' },
        { age: 32, name: 'Nakamura', teaching_subject: '英語', teaching_target: '3年生' }
      ]
    end
  end
end

module MixinSamples
  module TotalPrint

    def print_data
      puts convert_data
    end

    def print_names
      puts names
    end

    private

    def convert_data
      data.map { |val| val.map { |k, v| "#{k.capitalize}: #{v}" }.join(' | ') }
    end

    def names
      data.map { |val| val.values_at(:name) }.flatten.join("\n")
    end
  end
end

module MixinSamples
  module PersonalPrint

    def to_print
      puts person_info
    end

    private

    def person_info
      args.map { |k, v| "#{k.capitalize}: #{v}" }.join(' | ')
    end
  end
end

module MixinSamples
  module Search
    def search(name)
      objs = data.map { |hash| hash.values_at(:name).include?(name) ? hash : nil }.compact
      objs.map { |obj| new(obj) }
    end
  end
end

module MixinSamples
  class SchoolMember
    attr_accessor :args

    include PersonalPrint
    extend TotalPrint
    extend Search

    def initialize(args)
      @args = args
    end
  end
end

module MixinSamples
  class Teacher < SchoolMember
    include TeachersData
  end
end

module MixinSamples
  class Student < SchoolMember
    include StudentsData
  end
end

MixinSamples::Teacher.print_data
=>
Age: 46 | Name: Ito | Teaching_subject: 国語 | Teaching_target: 1年生
Age: 38 | Name: Watanabe | Teaching_subject: 数学 | Teaching_target: 2年生
Age: 25 | Name: Yamamoto | Teaching_subject: 科学 | Teaching_target: 3年生
Age: 32 | Name: Nakamura | Teaching_subject: 英語 | Teaching_target: 3年生

MixinSamples::Student.print_data
=>
Age: 18 | Name: Suzuki | Japanese: 70 | Math: 80 | Science: 90 | English: 70
Age: 17 | Name: Sato | Japanese: 60 | Math: 70 | Science: 50 | English: 50
Age: 18 | Name: Takahashi | Japanese: 90 | Math: 90 | Science: 100 | English: 70
Age: 16 | Name: Tanaka | Japanese: 80 | Math: 60 | Science: 70 | English: 90

teachers = MixinSamples::Teacher.search 'Ito'
=> [<MixinSamples::Teacher:0x007fd7b1682910 @age=46, @name="Ito", @teaching_subject="国語", @teaching_target="1年生">]

teachers.map { |teacher| teacher.to_print }
=>
Age: 46 | Name: Ito | Teaching_subject: 国語 | Teaching_target: 1年生

students = MixinSamples::Student.search 'Suzuki'
=> [<MixinSamples::Student:0x007fd7b1506500 @age=18, @args={:age=>18, :name=>"Suzuki", :japanese=>70, :math=>80, :science=>90, :english=>70}, @english=70, @japanese=70, @math=80, @name="Suzuki", @science=90>]

students.map { |student| student.to_print }
=>
Age: 18 | Name: Suzuki | Japanese: 70 | Math: 80 | Science: 90 | English: 70

class Duck < ActiveRecord:Base
  validates_length_of :name, maximum: 6
end

my_duck = Duck.new
my_duck.name = "Donald"
my_duck.valid? # => true
my_duck.save!


some_duck = Duck.first
some_duck.id   # => 1
some_duck.name # => "Donald"
some_duck.delete

# gems/activerecord-x.x.x/lib/active_record.rb
module ActiveRecord
  autoload :Base, 'active_record/base'
  autoload :Batches, 'active_record/batches'
  autoload :Calculations, 'active_record/calculations'
  autoload :Callbacks, 'active_record/callbacks'

  ・・・

end

module ActiveRecord
  class Base
    class << self
      def find(*args) # ...
      def first(*args) # ...
      def last(*args) # ...
      # ...
    end

    public
      def id # ...
      def save # ...
      def save! # ...
      def delete # ...
      # ...
  end
end

module ActiveRecord
  module Validations
    def self.included(base)
      base.extend ClassMethods
      base.class_eval do
        alias_method_chain :save, :validation
        alias_method_chain :save!, :validation
      end
      base.send :include, ActiveSupport::Callbacks
      # ...
    end

    module ClassMethods
      def validate_each(*attrs) # ...
      def validates_confirmation_of(*attr_names) # ...
      def validates_length_of(*attrs) # ...
      # ...
    end

    def save_with_validation(perform_validation = true) # ...
    def save_with_validation! # ...
    def valid? # ...
    # ...
  end
end

class MyClass
  def greet
    puts "Hello!"
  end
end

MyClass.new.greet # => Hello!

class MyClass
  def greet_with_log
    puts "メソッド呼び出し開始.."
    greet_without_log
    puts "...メソッド呼び出し完了"
  end

  alias_method :greet_without_log, :greet
  alias_method :greet, :greet_with_log
end

MyClass.new.greet
# =>
"メソッド呼び出し開始.."
"Hello!"
"...メソッド呼び出し完了""

module ActiveRecord
  module Validations
    def self.included(base)
      base.extend ClassMethods
      base.class_eval do
        alias_method_chain :save, :validation
        alias_method_chain :save!, :validation
      end

  ・・・

  end
end

array = [10, 20]
element = 30
eval("array << element") # => [10, 20, 30]

v1 = 1
eval("v1") # => 1

def my_method(method)
  eval("'a'.#{method}")
end

# 悪意のあるコード プライベートな情報が表示されてしまう。
my_method(object_id; Dir.glob("*")

'a'.object_id
Dir.glob("*")

user_input = "User input: #{gets()}"
# 汚染されているかどうかをチェック
puts user_input.tainted?

x = 1
true

# セーフレベルを１に設定
user_input = "User input: #{gets()}"
eval user_input

x = 1
# セーフレベル1以上の場合、汚染した文字列を評価できない
SecurityError: Insecure operatiion - eval

module MyModule
  # includedがフックメソッド 
  def self.included(othermod)
    # MyModuleが拡張されると下記が処理される
    puts "MyModuleは #{othermod}にmixinされた"
  end
end

class C
  include MyModule
end

# => MymoduleはCにmixinされた

class << an_object
　#処理を記述
end

eigenclass = class << obj
  self
end

eigenclass.class # => Class

class MyClass
  class << self
    def my_method; puts "Hello!" end
  end
end

MyClass.my_method # => "Hello!"
end

class MyClass
  # これだとインスタンスの属性定義になってしまう
  attr_accessor :a
end

MyClass.a # => NoMethodError: undefined method `a' for MyClass:Class
obj = MyClass.new
obj.a = 1
obj.a # => 1

class MyClass
  class << self
    attr_accessor :c
  end
end

MyClass.c = 'It works!'
MyClass.c # => "It works!"

module MyModule
  def my_method
    puts 1
  end
end

class MyClass
  class << self
    # 特異クラス内でインスタンスメソッドを拡張させるとクラスメソッドとして定義可能
    include MyModule
  end
end

MyClass.my_method # => 1

class MyClass
  extend MyModule
end

Myclass.my_method # => 1

alias :新しい名前 :古い名前

class MyClass
  def my_method; "my_method()"; end
  alias :my_method2 :my_method
end

m = MyClass.new()
m.my_method # =>  "my_method()"
m.my_method2 # =>  "my_method()"

class MyClass
  def my_method
    puts "original"
  end

  alias :my_method2 :my_method

  def my_method
    puts "changed"
  end
end

mc = MyClass.new
mc.my_method # => changed
mc.my_method2 # => original

class MyClass
  @my_var = 1
end

class MyClass
  @my_var = 1

  def self.read; @my_var; end
  def write; @my_var = 2; end
  def read; @my_var; end
end

obj = MyClass.new
obj.write
obj.read     # => 2
MyClass.read # => 1

class C
  @@v = 1
end

class D < C
  def my_method; @@v; end
end

D.new.my_method # => 1

@@v = 1

class MyClass
  @@v = 2
end

@@v # => 2

str = "just a regular string" # 普通の文字列

def str.title?
  self.upcase == self
end

str.title?                 # => false
str.methods.grep(/title?/) # => ["title?"]
str.singleton_methods      # => ["title?"]

# 特異メソッドの定義
def MyClass.class_method; end

# クラスメソッドの定義
class MyClass
  def self.class_method; end
end

def object.method
  # メソッドの中身
end

class Person
end

person = Person.new
person.name # => NoMethodError: undefined method `name' for #<Person:0x007f88d1cbbb58>

class Person
  def name
    @name
  end
end

person = Person.new
person.name        # => nil
person.name = 'Jo' # => NoMethodError: undefined method `name=' for #<Person:0x007f88d1ede5e8>

class Person
  def name
    @name
  end

  def name=(str)
    @name = str
  end
end

person = Person.new
person.name        # => nil
person.name = 'Jo' # => "Jo"
person.name        # => "Jo"

class Person
  attr_reader :name
  attr_writer :name
end

class Person
  attr_accessor :name

  def greeting
    "Hello, #{@name}"
  end
end

person = Person.new
person.name = 'Jo' # => "Jo"
person.greeting    # => "Hello, Jo"

class CandidatePanelCsvForm

    ・・・

  def self.model_name
    ActiveModel::Name.new(self, nil, "CandidatePanelCsvForm")
  end

    ・・・

end

module Csv
  class ResponseSetsService
    attr_accessor :filer

    def initialize(resource_owner, survey, **args)
      @resource_owner = resource_owner
      @survey         = survey
      @survey_group   = survey.group
      @args           = args
      @filer          = nil
    end

    ・・・

  end
end

module Missions
  class RecipientService
    attr_reader :burden

    delegate :commenter, to: :burden

    def initialize(burden)
      @burden = burden
    end

    ・・・

end

class Qualitative::SurveyGroupComment < ApplicationRecord

  ・・・

  private

  def notify_related_actors
    recipient_service = Missions::RecipientService.new(self)

    ・・・

  end

  ・・・

end

Missions::RecipientService.new(self).commenter

class MyClass
  def initialize
    @v = 1
  end

  def my_method
    private_method
  end

  private

  def private_method
    puts @v
  end
end

obj = MyClass.new
obj.my_method # => 1

v = 2
obj.instance_eval do
  @v = v
  def private_method
  puts @v + 1
end

obj.my_method # => 3

with_options on: [:update] do |v|
  v.validate :validate_relation_participants
  v.validates :group_id, presence: true, unless: Proc.new { owner.is_a?(Conceptor) } # ここ
  v.validates :not_send_from, presence: true
  v.validates :not_send_to, presence: true
end

# 遷移パターンを表示する
def visualize
  trees = []
  @tree.root_node.print_tree(0, nil, lambda { |node, prefix| trees << "#{prefix} #{node.name}" }) # ここ
  trees
end

v1 = 1

class MyClass
  v2 = 2
  local_variables # => [:v2]

  def my_method
    v3 = 3
    local_variables
  end

  local_variables # => [:v2]
end

obj = MyClass.new
obj.my_method # => [:v3]
obj.my_method # => [:v3]
local_variables # => [:v1, :obj]

my_var = "Success"

class MyClass
  # my_varを表示したい。。

  def my_method
    # my_varを表示したい！
  end
end

my_var = "Success"

MyClass = Class.new do
  puts "#{my_var} はクラスの中で表示できる！"

  define_method :my_method do
    puts "#{my_var} はメドッドの中で表示できる！"
  end
end

MyClass.new.my_method

# =>
Success はクラスの中で表示できる！
Success はメドッドの中で表示できる！

define_method :my_method do
  yield
end

my_method { puts "hello!" }
# => LocalJumpError: no block given (yield)

def my_method
  yield
end

my_method { puts "hello!" }
# =>
hello!

my_lambda = lambda{ puts "hello!" }

define_method :my_method, my_lambda
# =>
hello!

my_proc = proc{ puts "hello!" }

define_method :my_method, my_proc
# =>
hello!