shared_scope.rb

# ===================
# Spell: Shared Scope
# ===================

# Share variables among multiple contexts in the same Flat Scope (103).

lambda {
  shared = 10
  
  self.class.class_eval do
    define_method :counter do
      shared
    end
  
    define_method :down do
      shared -= 1
    end
  end
}.call

counter           # => 10
3.times { down }
counter           # => 7

# For more information: http://www.pragprog.com/titles/ppmetr/metaprogramming-ruby