Merge "FTL: Add Optional<T>::transform"

/*

 * 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

        "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",

/*

 * 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