Prevent MutableVectorData from being used for std::string.

PiperOrigin-RevId: 705972216

tensorflow_federated/cc/core/impl/aggregation/core/mutable_vector_data.h

@@ -20,17 +20,21 @@
 #include <cstddef>
 #include <memory>
 #include <string>
+#include <type_traits>
 #include <vector>
 
+#include "absl/strings/string_view.h"
 #include "tensorflow_federated/cc/core/impl/aggregation/core/tensor_data.h"
 
 namespace tensorflow_federated {
 namespace aggregation {
 
 // MutableVectorData implements TensorData by wrapping std::vector and using it
 // as a backing storage. MutableVectorData can be mutated using std::vector
-// methods.
-template <typename T>
+// methods. Use MutableStringData instead if the type is std::string.
+template <typename T, std::enable_if_t<std::is_arithmetic_v<T> ||
+                                           std::is_same_v<T, absl::string_view>,
+                                       int> = 0>
 class MutableVectorData : public std::vector<T>, public TensorData {
  public:
   // Derive constructors from the base vector class.