ForgottenVariable

class ForgetVariable(chainer.Variable):
    data_cache = None
    last_accessed_id = None

    def __init__(self, x):
        """
        :type x: chainer.Variable
        """
        self.rank = x.rank
        self._volatile = x._volatile

        self._grad = x._grad
        self.creator = x.creator
        self.name = x.name

        self._data = None
        if self.creator is not None:
            self.output_index = None
            for i, y in enumerate(self.creator.outputs):
                if y() is x:
                    self.output_index = i
            assert self.output_index is not None
            self.creator.outputs = tuple([weakref.ref(self) if id(y()) == id(x) else y
                                         for y in self.creator.outputs])

            ForgetVariable.data_cache = x.data
            ForgetVariable.last_accessed_id = id(self)
        else:
            self._data = x.data

    @property
    def data(self):
        if self._data is not None:
            return self._data

        if ForgetVariable.last_accessed_id == id(self):
            return ForgetVariable.data_cache

        in_data = tuple([x.data for x in self.creator.inputs])
        out_data = self.creator.forward(in_data)[self.output_index]
        ForgetVariable.data_cache = out_data
        ForgetVariable.last_accessed_id = id(self)

        return out_data