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diff --git a/include/ftl/initializer_list.h b/include/ftl/initializer_list.h
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+++ b/include/ftl/initializer_list.h
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+/*
+ * Copyright 2020 The Android Open Source Project
+ *
+ * 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
+ *
+ *      http://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.
+ */
+
+#pragma once
+
+#include <tuple>
+#include <utility>
+
+namespace android::ftl {
+
+// Compile-time counterpart of std::initializer_list<T> that stores per-element constructor
+// arguments with heterogeneous types. For a container with elements of type T, given Sizes
+// (S0, S1, ..., SN), N elements are initialized: the first element is initialized with the
+// first S0 arguments, the second element is initialized with the next S1 arguments, and so
+// on. The list of Types (T0, ..., TM) is flattened, so M is equal to the sum of the Sizes.
+//
+// An InitializerList is created using ftl::init::list, and is consumed by constructors of
+// containers. The function call operator is overloaded such that arguments are accumulated
+// in a tuple with each successive call. For instance, the following calls initialize three
+// strings using different constructors, i.e. string literal, default, and count/character:
+//
+//   ... = ftl::init::list<std::string>("abc")()(3u, '?');
+//
+// The following syntax is a shorthand for key-value pairs, where the first argument is the
+// key, and the rest construct the value. The types of the key and value are deduced if the
+// first pair contains exactly two arguments:
+//
+//   ... = ftl::init::map<int, std::string>(-1, "abc")(-2)(-3, 3u, '?');
+//
+//   ... = ftl::init::map(0, 'a')(1, 'b')(2, 'c');
+//
+// WARNING: The InitializerList returned by an ftl::init::list expression must be consumed
+// immediately, since temporary arguments are destroyed after the full expression. Storing
+// an InitializerList results in dangling references.
+//
+template <typename T, typename Sizes = std::index_sequence<>, typename... Types>
+struct InitializerList;
+
+template <typename T, std::size_t... Sizes, typename... Types>
+struct InitializerList<T, std::index_sequence<Sizes...>, Types...> {
+  // Creates a superset InitializerList by appending the number of arguments to Sizes, and
+  // expanding Types with forwarding references for each argument.
+  template <typename... Args>
+  [[nodiscard]] constexpr auto operator()(Args&&... args) && -> InitializerList<
+      T, std::index_sequence<Sizes..., sizeof...(Args)>, Types..., Args&&...> {
+    return {std::tuple_cat(std::move(tuple), std::forward_as_tuple(std::forward<Args>(args)...))};
+  }
+
+  // The temporary InitializerList returned by operator() is bound to an rvalue reference in
+  // container constructors, which extends the lifetime of any temporary arguments that this
+  // tuple refers to until the completion of the full expression containing the construction.
+  std::tuple<Types...> tuple;
+};
+
+template <typename K, typename V>
+struct KeyValue {};
+
+// Shorthand for key-value pairs that assigns the first argument to the key, and the rest to the
+// value. The specialization is on KeyValue rather than std::pair, so that ftl::init::list works
+// with the latter.
+template <typename K, typename V, std::size_t... Sizes, typename... Types>
+struct InitializerList<KeyValue<K, V>, std::index_sequence<Sizes...>, Types...> {
+  // Accumulate the three arguments to std::pair's piecewise constructor.
+  template <typename... Args>
+  [[nodiscard]] constexpr auto operator()(K&& k, Args&&... args) && -> InitializerList<
+      KeyValue<K, V>, std::index_sequence<Sizes..., 3>, Types..., std::piecewise_construct_t,
+      std::tuple<K&&>, std::tuple<Args&&...>> {
+    return {std::tuple_cat(
+        std::move(tuple),
+        std::forward_as_tuple(std::piecewise_construct, std::forward_as_tuple(std::forward<K>(k)),
+                              std::forward_as_tuple(std::forward<Args>(args)...)))};
+  }
+
+  std::tuple<Types...> tuple;
+};
+
+namespace init {
+
+template <typename T, typename... Args>
+[[nodiscard]] constexpr auto list(Args&&... args) {
+  return InitializerList<T>{}(std::forward<Args>(args)...);
+}
+
+template <typename K, typename V, typename... Args>
+[[nodiscard]] constexpr auto map(Args&&... args) {
+  return list<KeyValue<K, V>>(std::forward<Args>(args)...);
+}
+
+template <typename K, typename V>
+[[nodiscard]] constexpr auto map(K&& k, V&& v) {
+  return list<KeyValue<K, V>>(std::forward<K>(k), std::forward<V>(v));
+}
+
+}  // namespace init
+}  // namespace android::ftl