C++ API: Added a Const constructor for non-empty const supporting type cast.

Fixes #3752
Change: 130113000

2 files changed, 33 insertions, 13 deletions

diff --git a/tensorflow/cc/ops/const_op.h b/tensorflow/cc/ops/const_op.h
index 75844d124d..8976a24edc 100644
--- a/tensorflow/cc/ops/const_op.h
+++ b/tensorflow/cc/ops/const_op.h
@@ -25,22 +25,35 @@ namespace ops {
 
 Output Const(const Scope& scope, const Input::Initializer& val);
 
+NodeBuilder::NodeOut AsNodeOut(const Scope& scope, const Input& inp);
+
 template <typename T>
 Output Const(const Scope& scope, const Input::Initializer& val) {
+  auto orig_const_output = Const(scope, val);
   if (!scope.ok()) return Output();
-  if (!val.status.ok()) {
-    scope.UpdateStatus(val.status);
-    return Output();
-  }
+
   typedef typename Input::Initializer::RealType<T>::type DstT;
-  if (val.tensor.NumElements() > 0) {
-    // TODO(keveman): Implement the in-situ cast.
-    scope.UpdateStatus(errors::Unimplemented(
-        "Explict cast of a non-empty tensor not implemented yet"));
-    return Output();
+
+  if (val.tensor.dtype() == DataTypeToEnum<DstT>::v()) {
+    return orig_const_output;
   }
-  Tensor t(DataTypeToEnum<DstT>::v(), val.tensor.shape());
-  return Const(scope, Input::Initializer(t));
+  if (val.tensor.NumElements() == 0) {
+    Tensor t(DataTypeToEnum<DstT>::v(), val.tensor.shape());
+    return Const(scope, Input::Initializer(t));
+  }
+
+  // TODO(keveman): Refactor Cast op's kernel implementation such that the code
+  // can be directly called here instead of adding the Cast op to the graph.
+  auto orig_const = AsNodeOut(scope, orig_const_output);
+  const auto cast_op_name = scope.GetUniqueNameForOp("Cast");
+
+  auto cast_builder = NodeBuilder(cast_op_name, "Cast")
+                          .Input(orig_const)
+                          .Attr("DstT", DataTypeToEnum<DstT>::v());
+  scope.UpdateBuilder(&cast_builder);
+  Node* ret;
+  scope.UpdateStatus(cast_builder.Finalize(scope.graph(), &ret));
+  return Output(ret, 0);
 }
 
 template <typename T>
@@ -54,8 +67,6 @@ Output Const(const Scope& scope, const std::initializer_list<T>& v,
   return Const(scope, Input::Initializer(v, shape));
 }
 
-NodeBuilder::NodeOut AsNodeOut(const Scope& scope, const Input& inp);
-
 std::vector<NodeBuilder::NodeOut> AsNodeOutList(const Scope& scope,
                                                 const InputList& inp);
 
diff --git a/tensorflow/cc/ops/const_op_test.cc b/tensorflow/cc/ops/const_op_test.cc
index a56b66c1cc..5a4770f879 100644
--- a/tensorflow/cc/ops/const_op_test.cc
+++ b/tensorflow/cc/ops/const_op_test.cc
@@ -125,4 +125,13 @@ TEST(ConstOpTest, Names) {
   EXPECT_EQ(c_y_1.node()->name(), "c/y_1");
 }
 
+TEST(ConstOpTest, TemplatedConst) {
+  Scope root = Scope::NewRootScope();
+  auto c1 = ops::Const<int>(root, {1, 2});
+  ExpectTypeAndShape(c1.node(), DT_INT32, {2});
+
+  auto c2 = ops::Const<string>(root, {{"this"}, {"is"}, {"a"}, {"constant"}});
+  ExpectTypeAndShape(c2.node(), DT_STRING, {4, 1});
+}
+
 }  // namespace tensorflow