FTL: Add Optional<T>::transform
Bug: 185536303
Test: ftl_test
Change-Id: If4cb9894c615499af04bb9793d9f900485e18fe2
diff --git a/include/ftl/optional.h b/include/ftl/optional.h
new file mode 100644
index 0000000..daf4502
--- /dev/null
+++ b/include/ftl/optional.h
@@ -0,0 +1,71 @@
+/*
+ * Copyright 2022 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 <functional>
+#include <optional>
+#include <type_traits>
+#include <utility>
+
+namespace android::ftl {
+
+// Superset of std::optional<T> with monadic operations, as proposed in https://wg21.link/P0798R8.
+//
+// TODO: Remove in C++23.
+//
+template <typename T>
+struct Optional final : std::optional<T> {
+ using std::optional<T>::optional;
+
+ using std::optional<T>::has_value;
+ using std::optional<T>::value;
+
+ // Returns Optional<U> where F is a function that maps T to U.
+ template <typename F>
+ constexpr auto transform(F&& f) const& {
+ using U = std::remove_cv_t<std::invoke_result_t<F, decltype(value())>>;
+ if (has_value()) return Optional<U>(std::invoke(std::forward<F>(f), value()));
+ return Optional<U>();
+ }
+
+ template <typename F>
+ constexpr auto transform(F&& f) & {
+ using U = std::remove_cv_t<std::invoke_result_t<F, decltype(value())>>;
+ if (has_value()) return Optional<U>(std::invoke(std::forward<F>(f), value()));
+ return Optional<U>();
+ }
+
+ template <typename F>
+ constexpr auto transform(F&& f) const&& {
+ using U = std::invoke_result_t<F, decltype(std::move(value()))>;
+ if (has_value()) return Optional<U>(std::invoke(std::forward<F>(f), std::move(value())));
+ return Optional<U>();
+ }
+
+ template <typename F>
+ constexpr auto transform(F&& f) && {
+ using U = std::invoke_result_t<F, decltype(std::move(value()))>;
+ if (has_value()) return Optional<U>(std::invoke(std::forward<F>(f), std::move(value())));
+ return Optional<U>();
+ }
+};
+
+// Deduction guide.
+template <typename T>
+Optional(T) -> Optional<T>;
+
+} // namespace android::ftl
diff --git a/libs/ftl/Android.bp b/libs/ftl/Android.bp
index c010a2e..8f89e7d 100644
--- a/libs/ftl/Android.bp
+++ b/libs/ftl/Android.bp
@@ -20,6 +20,7 @@
"fake_guard_test.cpp",
"flags_test.cpp",
"future_test.cpp",
+ "optional_test.cpp",
"small_map_test.cpp",
"small_vector_test.cpp",
"static_vector_test.cpp",
diff --git a/libs/ftl/optional_test.cpp b/libs/ftl/optional_test.cpp
new file mode 100644
index 0000000..6a8c8f9
--- /dev/null
+++ b/libs/ftl/optional_test.cpp
@@ -0,0 +1,77 @@
+/*
+ * Copyright 2022 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.
+ */
+
+#include <ftl/optional.h>
+#include <ftl/static_vector.h>
+#include <ftl/string.h>
+#include <gtest/gtest.h>
+
+#include <functional>
+#include <numeric>
+#include <utility>
+
+using namespace std::placeholders;
+using namespace std::string_literals;
+
+namespace android::test {
+
+using ftl::Optional;
+using ftl::StaticVector;
+
+TEST(Optional, Transform) {
+ // Empty.
+ EXPECT_EQ(std::nullopt, Optional<int>().transform([](int) { return 0; }));
+
+ // By value.
+ EXPECT_EQ(0, Optional(0).transform([](int x) { return x; }));
+ EXPECT_EQ(100, Optional(99).transform([](int x) { return x + 1; }));
+ EXPECT_EQ("0b100"s, Optional(4).transform(std::bind(ftl::to_string<int>, _1, ftl::Radix::kBin)));
+
+ // By reference.
+ {
+ Optional opt = 'x';
+ EXPECT_EQ('z', opt.transform([](char& c) {
+ c = 'y';
+ return 'z';
+ }));
+
+ EXPECT_EQ('y', opt);
+ }
+
+ // By rvalue reference.
+ {
+ std::string out;
+ EXPECT_EQ("xyz"s, Optional("abc"s).transform([&out](std::string&& str) {
+ out = std::move(str);
+ return "xyz"s;
+ }));
+
+ EXPECT_EQ(out, "abc"s);
+ }
+
+ // Chaining.
+ EXPECT_EQ(14u, Optional(StaticVector{"upside"s, "down"s})
+ .transform([](StaticVector<std::string, 3>&& v) {
+ v.push_back("cake"s);
+ return v;
+ })
+ .transform([](const StaticVector<std::string, 3>& v) {
+ return std::accumulate(v.begin(), v.end(), std::string());
+ })
+ .transform([](const std::string& s) { return s.length(); }));
+}
+
+} // namespace android::test