static const char* const kRetValOp = "_Retval";

class Encapsulator {
 public:
  Encapsulator(string group_attribute, Graph const* graph_in)
      : group_attribute_(std::move(group_attribute)), graph_in_(graph_in) {}

  // Find subgraphs marked with 'group_attribute', and build a new
  // subgraph, one for each value of 'group_attribute'.
  Status SplitIntoSubgraphs(FunctionLibraryDefinition* library);

    std::vector<int>* output_permutation, NodeDef* node_def)>
    RewriteSubgraphFn;

// Transformation that finds subgraphs whose nodes are marked with
// 'group_attribute', splits those subgraphs into functions, and replaces
// the originals with function calls.
//
// 'group_attribute' must be a string valued-attribute that names the new
// functions to introduce.
//
// If 'rewrite_subgraph_fn' is set, it is applied to each subgraph before