module Tins::ThreadLocal

def instance_thread_local(name, default_value = nil, &default)
  class << self
    extend Tins::ThreadLocal
    self
  end.thread_local name, default_value, &default
  self
end

def thread_local(name, default_value = nil, &default)
  is_a?(Module) or raise TypeError, "receiver has to be a Module"
  default_value && default and raise ArgumentError,
    "require either default_falue or default block"
  if default_value
    default = -> * { default_value }
  end
  name = name.to_s
  my_id = "__thread_local_#{__id__}__"
  ObjectSpace.define_finalizer(self, @@cleanup)
  define_method(name) do
    values = Thread.current[my_id] ||= {}
    if default && !values.key?(name)
      values[name] = default.call
    end
    values[name]
  end
  define_method("#{name}=") do |value|
    Thread.current[my_id] ||= {}
    Thread.current[my_id][name] = value
  end
  self
end