From ecb46023f65964fc02c3eb97ee9821b55cc24c43 Mon Sep 17 00:00:00 2001
From: Sujin Philip <sujin.philip@kitware.com>
Date: Thu, 21 Jun 2018 13:35:57 -0400
Subject: [PATCH] Add ListTagAppend and ListTagAppendUnique

---
 vtkm/ListTag.h                   | 16 ++++++++++++++++
 vtkm/internal/ListTagDetail.h    |  9 ++++++++-
 vtkm/testing/UnitTestListTag.cxx | 21 +++++++++++++++++++++
 3 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/vtkm/ListTag.h b/vtkm/ListTag.h
index 46ef653a0..b78691280 100644
--- a/vtkm/ListTag.h
+++ b/vtkm/ListTag.h
@@ -73,6 +73,22 @@ struct ListTagJoin : detail::ListRoot
   using list = typename detail::ListJoin<typename ListTag1::list, typename ListTag2::list>::type;
 };
 
+
+/// A tag that is constructed by appending \c Type to \c ListTag.
+template <typename ListTag, typename Type>
+struct ListTagAppend : detail::ListRoot
+{
+  using list = typename detail::ListJoin<typename ListTag::list, detail::ListBase<Type>>::type;
+};
+
+/// Append \c Type to \c ListTag only if \c ListTag does not already contain \c Type.
+/// No checks are performed to see if \c ListTag itself has only unqiue elements.
+template <typename ListTag, typename Type>
+struct ListTagAppendUnique : detail::ListRoot
+{
+  using list = typename detail::ListAppendUniqueImpl<typename ListTag::list, Type>::type;
+};
+
 /// A tag that consists of elements that are found in both tags. This struct
 /// can be subclassed and still behave like a list tag.
 template <typename ListTag1, typename ListTag2>
diff --git a/vtkm/internal/ListTagDetail.h b/vtkm/internal/ListTagDetail.h
index cae6b80f8..3cb66236d 100644
--- a/vtkm/internal/ListTagDetail.h
+++ b/vtkm/internal/ListTagDetail.h
@@ -229,7 +229,14 @@ struct ListCrossProductImpl
           brigand::lazy::push_front<brigand::_1, brigand::parent<brigand::_1>>>>>>>>>>;
 };
 
-
+//-----------------------------------------------------------------------------
+template <typename List, typename Type>
+struct ListAppendUniqueImpl
+{
+  using type = typename std::conditional<ListContainsImpl<Type, List>::value,
+                                         List,
+                                         typename ListJoin<List, ListBase<Type>>::type>::type;
+};
 
 } // namespace detail
 
diff --git a/vtkm/testing/UnitTestListTag.cxx b/vtkm/testing/UnitTestListTag.cxx
index 284619d17..29185902a 100644
--- a/vtkm/testing/UnitTestListTag.cxx
+++ b/vtkm/testing/UnitTestListTag.cxx
@@ -67,6 +67,18 @@ struct TestListTagUniversal : vtkm::ListTagUniversal
 {
 };
 
+struct TestListTagAppend : vtkm::ListTagAppend<TestListTag3, TestClass<34>>
+{
+};
+
+struct TestListTagAppendUnique1 : vtkm::ListTagAppendUnique<TestListTag3, TestClass<32>>
+{
+};
+
+struct TestListTagAppendUnique2 : vtkm::ListTagAppendUnique<TestListTagAppendUnique1, TestClass<34>>
+{
+};
+
 template <int N, int M>
 std::pair<int, int> test_number(brigand::list<TestClass<N>, TestClass<M>>)
 {
@@ -239,6 +251,15 @@ void TestLists()
   TryList(vtkm::Vec<std::pair<int, int>, 3>({ 31, 11 }, { 32, 11 }, { 33, 11 }),
           TestListTagCrossProduct());
 
+  std::cout << "ListTagAppend" << std::endl;
+  TryList(vtkm::Vec<int, 4>(31, 32, 33, 34), TestListTagAppend());
+
+  std::cout << "ListTagAppendUnique1" << std::endl;
+  TryList(vtkm::Vec<int, 3>(31, 32, 33), TestListTagAppendUnique1());
+
+  std::cout << "ListTagAppendUnique2" << std::endl;
+  TryList(vtkm::Vec<int, 4>(31, 32, 33, 34), TestListTagAppendUnique2());
+
 
 
   std::cout << "ListTagUniversal" << std::endl;