Instance variable with EventMachine module

I hope this helps you . As I say there was something that I was missing.
You can add parameters for class to be instantiated :

  class Server< EM::Connection
    def initialize par
       puts "I'm server number#{par}"
    end
    def receive_data data
      send_data data
      close_connection_after_writing
    end
 end

EventMachine.run {
  EventMachine.start_server '127.0.0.1','8080', Server,1
}

EventMachine.run {
  EventMachine.start_server '127.0.0.1','8080', Server,2
}

should help you out Because @myg is not shared variable. It is private property of module Test, thus while you included Test, @myg didn't come into Xy due to the mixin, it wouldn't come also by default. But, "Why nil?" - Because, instance variable, class variables are like that. Before initialising/defining them, if you attempt to use them, it will simply give you nil.
Small program to prove myself and Ruby :-

module Test
  @x = 10
  @@y = 11
end

class Foo
  include Test
end

Foo.instance_variable_defined?(:@x) # => false
Test.instance_variable_defined?(:@x) # => true
Foo.class_variable_defined?(:@@y) # => true
Test.class_variable_defined?(:@@y) # => true

module Test
  class << self
    attr_reader :myg
  end

  RED = "rose"
  BLUE = "ivy"
  @myg = 9
  @@vit = 24.6
end

class Xy
  include Test

  def initialize(n)
    @garb = n
  end

  attr_accessor :garb

  def garbTest
    @garb = Test.myg
  end

  def exo
    return 50
  end
end

ryu = Xy.new(16)
ryu.garbTest # => 9

like below fixes the issue Instance variables are called instance variables, because they belong to objects (aka "instances"). There are two objects in your example: SomeModule and Reporter. Both have their own instance variables. SomeModule has an instance variable named @param and Reporter has an instance variable named @param. Those two instance variables are completely unrelated, even though the have the same name. Imagine the chaos, if every object had to come up with its own names for instance variables!

module SomeModule
  def self.param; @param end
  @param = 'Hello'
end

module Reporter
  def self.put
    puts SomeModule.param
  end
end

module SomeModule
  class << self; attr_reader :param end
  @param = 'Hello'
end

module Reporter
  def self.put
    puts SomeModule.param
  end
end

module SomeModule
  class << self
    attr_reader :param

    private

    def param=(param)
      @param = param
    end
  end

  self.param = 'Hello'
end

module Reporter
  def self.put
    puts SomeModule.param
  end
end

module SomeModule
  class << self
    attr_reader :param

    private

    attr_writer :param
  end

  self.param = 'Hello'
end

module Reporter
  def self.put
    puts SomeModule.param
  end
end

Any of those help Because you mapped a function as unbound method of A, so when you are calling cls.func you first ask something equals to getattr(cls, 'func') which returns BUT, this unbound method needs to be called with class as first argument.
So because in this specific case cls.func means "gives me class attribute func of cls" it can not means to the same time "call class method func" - So Python doesn't translate cls.func() by func(cls).

@classmethod
def test(cls):
    print getattr(cls, 'func') # <unbound method A.task>

def task(cls=None):
    if cls is None:
        print 'task()'
    else:
        print 'A.foo({})'.format(cls)

a = task

class A:
    func = task             # this show error unbound method

    def __init__(self):
        self.func_1 = task

    def test_1(self):
        self.func_1()

    @classmethod
    def test(cls):
        cls.func(cls())

a()
A().test_1()
A.test()

task()
task()
A.foo(<__main__.A instance at 0x7fd0310a46c8>)

it should still fix some issue This roughly means that if @current_user, as an instance variable of global request/response scope (Controller/View/Helpers), has already been defined, use it as current_user. Otherwise, assign it the user that corresponds to the id stored in the session do what you do.
In other words, this is similar to:

def current_user
    if @current_user # this will be false in every hit, for the same request
        @current_user
    else
        User.find_by id: session[:user_id]
    end
end

def current_user
    if @current_user # this will be false for the first hit, true for every subsequent request
        @current_user 
    else
        @current_user = User.find_by id: session[:user_id]
    end
end

def current_user
    @current_user ||= User.find_by id: session[:user_id]
end