Local static variable in Ruby

local_static_variable3.rb

module Static
  cache = ""
  klass = class<<self; self; end
  klass.send(:define_method, :foo) do
    lambda {|s| cache += s; cache }
  end

  def self.out_of_scope
    cache
  rescue
    "you cannot see cache"
  end
end

f = Static.foo
f.call "hello"
f.call ", "
f.call "world"

module Say
  def self.hello
    f = Static.foo
    f.call("!")
  end
end

puts Say.hello #=> "hello, world!"
puts Static.out_of_scope #=> "you cannot see cache"