         case TF_VARIANT: return "variant"
         case TF_UINT32: return "uint32"
         case TF_UINT64: return "uint64"
-        default: assert(false, "Unhandled type: \(cDataType)")
+        default: fatalError("Unhandled type: \(cDataType)")
         }
     }
 }

    func updateAttribute<In: TensorGroup, Out: TensorGroup>(
        _ name: String, _ value: (In) -> Out) {
        // TODO:
        assert(false, "Unimplemented [TFFunction] attribute.")
    }

    func execute() {}

        case .concrete(let h, _):
            return h
        case .symbolic(_, _, _):
            fatalError("TODO: to be send out in a separate PR.")
            // return op.materialized(index: index)
        }
    }
