You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: Boxes.rb
    path of file: ./repos/sorbet/test/testdata/infer/generics
    
    the code of the file until where you have to start completion: # typed: true

def _; end

class Box
  ext
    
def _; end

class Box
  extend T::Generic
  extend T::Sig

  A = type_member

  def initialize
    @value = T.let(T.unsafe(nil), A)
  end

   sig {params(value: A).returns(NilClass)}
   def store(value)
     @value = value
     nil
   end

   sig {returns(A)}
   def read
     @value
   end
end