def sg_rnn_layer_func(func):
    r"""Decorates function as sg_rnn_layer functions.
    Args:
        func: function to decorate
    """
    @wraps(func)
    def wrapper(tensor, **kwargs):
        r"""Manages arguments of `tf.sg_opt`.

        Args:
          tensor: automatically passed by decorator
          kwargs:
              in_dim: An integer. The size of input dimension, which is set to the last one by default.
              dim: An integer. The size of output dimension. Has the same value as in_dim by default.
              ln: Boolean. If True, layer normalization is applied.
              bias: Boolean. If True, biases are added. As a default, it is set to True
              name: A name for the layer. As a default, the function name is assigned.
              reuse: `True` or `None`; if `True`, we go into reuse mode for this `layer` scope
                as well as all sub-scopes; if `None`, we just inherit the parent scope reuse.
              summary: If True, summaries are added. The default is True.
        """

        # kwargs parsing
        opt = tf.sg_opt(kwargs) + sg_get_context()

        # set default argument
        try:
            shape = tensor.get_shape().as_list()
            # dropout off
            opt += tf.sg_opt(shape=shape, in_dim=shape[-1], dim=shape[-1], dout=0, summary=True)
            # disable bias when normalization on
            opt += tf.sg_opt(bias=not opt.ln)
        finally:
            pass

        # automatic layer naming
        if opt.name is None:

            # layer function name will be used as layer name
            opt.name = func.__name__.replace('sg_', '')

            # find existing layer names
            exist_layers = []
            for t in tf.global_variables():
                scope_name = tf.get_variable_scope().name
                prefix = scope_name + '/' if len(scope_name) > 0 else ''
                i = t.name.rfind(prefix + opt.name)
                if i >= 0:
                    exist_layers.append(t.name[i:].split('/')[-2])
            exist_layers = list(set(exist_layers))

            # layer name numbering
            if len(exist_layers) == 0:
                opt.name += '_1'
            else:
                opt.name += '_%d' % (max([int(n.split('_')[-1]) for n in exist_layers]) + 1)

        with tf.variable_scope(opt.name, reuse=opt.reuse) as scope:

            # call layer function
            out = func(tensor, opt)

            # apply dropout
            if opt.dout:
                out = tf.cond(_phase,
                              lambda: tf.nn.dropout(out, 1 - opt.dout),
                              lambda: out)

            # rename tensor
            out = tf.identity(out, 'out')

            # add final output summary
            if opt.summary:
                tf.sg_summary_activation(out)

            # save node info for reuse
            out._sugar = tf.sg_opt(func=func, arg=tf.sg_opt(kwargs) + sg_get_context(),
                                   prev=tensor, is_layer=True, name=opt.name)
            # inject reuse function
            out.sg_reuse = types.MethodType(sg_reuse, out)

        return out

    return wrapper