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diff --git a/include/dap/variant.h b/include/dap/variant.h
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+++ b/include/dap/variant.h
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+// Copyright 2019 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef dap_variant_h
+#define dap_variant_h
+
+#include "any.h"
+
+namespace dap {
+
+// internal functionality
+namespace detail {
+template <typename T, typename...>
+struct TypeIsIn {
+  static constexpr bool value = false;
+};
+
+template <typename T, typename List0, typename... ListN>
+struct TypeIsIn<T, List0, ListN...> {
+  static constexpr bool value =
+      std::is_same<T, List0>::value || TypeIsIn<T, ListN...>::value;
+};
+}  // namespace detail
+
+// variant represents a type-safe union of DAP types.
+// variant can hold a value of any of the template argument types.
+// variant defaults to a default-constructed T0.
+template <typename T0, typename... Types>
+class variant {
+ public:
+  // constructors
+  inline variant();
+  template <typename T>
+  inline variant(const T& val);
+
+  // assignment
+  template <typename T>
+  inline variant& operator=(const T& val);
+
+  // get() returns the contained value of the type T.
+  // If the any does not contain a value of type T, then get() will assert.
+  template <typename T>
+  inline T& get() const;
+
+  // is() returns true iff the contained value is of type T.
+  template <typename T>
+  inline bool is() const;
+
+  // accepts() returns true iff the variant accepts values of type T.
+  template <typename T>
+  static constexpr bool accepts();
+
+ private:
+  friend class Serializer;
+  friend class Deserializer;
+  any value;
+};
+
+template <typename T0, typename... Types>
+variant<T0, Types...>::variant() : value(T0()) {}
+
+template <typename T0, typename... Types>
+template <typename T>
+variant<T0, Types...>::variant(const T& v) : value(v) {
+  static_assert(accepts<T>(), "variant does not accept template type T");
+}
+
+template <typename T0, typename... Types>
+template <typename T>
+variant<T0, Types...>& variant<T0, Types...>::operator=(const T& v) {
+  static_assert(accepts<T>(), "variant does not accept template type T");
+  value = v;
+  return *this;
+}
+
+template <typename T0, typename... Types>
+template <typename T>
+T& variant<T0, Types...>::get() const {
+  static_assert(accepts<T>(), "variant does not accept template type T");
+  return value.get<T>();
+}
+
+template <typename T0, typename... Types>
+template <typename T>
+bool variant<T0, Types...>::is() const {
+  return value.is<T>();
+}
+
+template <typename T0, typename... Types>
+template <typename T>
+constexpr bool variant<T0, Types...>::accepts() {
+  return detail::TypeIsIn<T, T0, Types...>::value;
+}
+
+}  // namespace dap
+
+#endif  // dap_variant_h