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Commit a957c1c1 authored by Dominik Laskowski's avatar Dominik Laskowski
Browse files

FTL: Add Optional<T>::and_then 

Bug: 185536303
Test: ftl_test
Change-Id: Ic907a662a2090ad1363bd329e7d758b2acef55ad
parent 76c33b19

include/ftl/details/optional.h

0 → 100644
+58 −0
Original line number Diff line number Diff line 
/*

 * 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 <ftl/details/type_traits.h>



namespace android::ftl {



template <typename>

struct Optional;



namespace details {



template <typename>

struct is_optional : std::false_type {};



template <typename T>

struct is_optional<std::optional<T>> : std::true_type {};



template <typename T>

struct is_optional<Optional<T>> : std::true_type {};



template <typename F, typename T>

struct transform_result {

  using type = Optional<std::remove_cv_t<std::invoke_result_t<F, T>>>;

};



template <typename F, typename T>

using transform_result_t = typename transform_result<F, T>::type;



template <typename F, typename T>

struct and_then_result {

  using type = remove_cvref_t<std::invoke_result_t<F, T>>;

  static_assert(is_optional<type>{}, "and_then function must return an optional");

};



template <typename F, typename T>

using and_then_result_t = typename and_then_result<F, T>::type;



}  // namespace details

}  // namespace android::ftl

include/ftl/details/type_traits.h

0 → 100644
+27 −0
Original line number Diff line number Diff line 
/*

 * 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 <type_traits>



namespace android::ftl::details {



// TODO: Replace with std::remove_cvref_t in C++20.

template <typename U>

using remove_cvref_t = std::remove_cv_t<std::remove_reference_t<U>>;



}  // namespace android::ftl::details

include/ftl/optional.h

+43 −13
Original line number Diff line number Diff line
@@ -18,9 +18,10 @@ 


#include <functional>

#include <optional>

#include <type_traits>

#include <utility>



#include <ftl/details/optional.h>



namespace android::ftl {



// Superset of std::optional<T> with monadic operations, as proposed in https://wg21.link/P0798R8.
@@ -37,30 +38,59 @@ struct Optional final : std::optional<T> { 
  // 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>();

    using R = details::transform_result_t<F, decltype(value())>;

    if (has_value()) return R(std::invoke(std::forward<F>(f), value()));

    return R();

  }



  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>();

    using R = details::transform_result_t<F, decltype(value())>;

    if (has_value()) return R(std::invoke(std::forward<F>(f), value()));

    return R();

  }



  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>();

    using R = details::transform_result_t<F, decltype(std::move(value()))>;

    if (has_value()) return R(std::invoke(std::forward<F>(f), std::move(value())));

    return R();

  }



  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>();

    using R = details::transform_result_t<F, decltype(std::move(value()))>;

    if (has_value()) return R(std::invoke(std::forward<F>(f), std::move(value())));

    return R();

  }



  // Returns Optional<U> where F is a function that maps T to Optional<U>.

  template <typename F>

  constexpr auto and_then(F&& f) const& {

    using R = details::and_then_result_t<F, decltype(value())>;

    if (has_value()) return std::invoke(std::forward<F>(f), value());

    return R();

  }



  template <typename F>

  constexpr auto and_then(F&& f) & {

    using R = details::and_then_result_t<F, decltype(value())>;

    if (has_value()) return std::invoke(std::forward<F>(f), value());

    return R();

  }



  template <typename F>

  constexpr auto and_then(F&& f) const&& {

    using R = details::and_then_result_t<F, decltype(std::move(value()))>;

    if (has_value()) return std::invoke(std::forward<F>(f), std::move(value()));

    return R();

  }



  template <typename F>

  constexpr auto and_then(F&& f) && {

    using R = details::and_then_result_t<F, decltype(std::move(value()))>;

    if (has_value()) return std::invoke(std::forward<F>(f), std::move(value()));

    return R();

  }

};

include/ftl/small_vector.h

+3 −6
Original line number Diff line number Diff line
@@ -21,11 +21,12 @@ 


#include <algorithm>

#include <iterator>

#include <type_traits>

#include <utility>

#include <variant>

#include <vector>



#include <ftl/details/type_traits.h>



namespace android::ftl {



template <typename>
@@ -80,10 +81,6 @@ class SmallVector final : details::ArrayTraits<T>, details::ArrayComparators<Sma 
  using Static = StaticVector<T, N>;

  using Dynamic = SmallVector<T, 0>;



  // TODO: Replace with std::remove_cvref_t in C++20.

  template <typename U>

  using remove_cvref_t = std::remove_cv_t<std::remove_reference_t<U>>;



 public:

  FTL_ARRAY_TRAIT(T, value_type);

  FTL_ARRAY_TRAIT(T, size_type);
@@ -104,7 +101,7 @@ class SmallVector final : details::ArrayTraits<T>, details::ArrayComparators<Sma 


  // Constructs at most N elements. See StaticVector for underlying constructors.

  template <typename Arg, typename... Args,

            typename = std::enable_if_t<!is_small_vector<remove_cvref_t<Arg>>{}>>

            typename = std::enable_if_t<!is_small_vector<details::remove_cvref_t<Arg>>{}>>

  SmallVector(Arg&& arg, Args&&... args)

      : vector_(std::in_place_type<Static>, std::forward<Arg>(arg), std::forward<Args>(args)...) {}

libs/ftl/optional_test.cpp

+59 −0
Original line number Diff line number Diff line
@@ -20,6 +20,7 @@ 
#include <ftl/unit.h>

#include <gtest/gtest.h>



#include <cstdlib>

#include <functional>

#include <numeric>

#include <utility>
@@ -82,4 +83,62 @@ TEST(Optional, Transform) { 
                     .transform([](const std::string& s) { return s.length(); }));

}



namespace {



Optional<int> parse_int(const std::string& str) {

  if (const int i = std::atoi(str.c_str())) return i;

  return std::nullopt;

}



}  // namespace



TEST(Optional, AndThen) {

  // Empty.

  EXPECT_EQ(std::nullopt, Optional<int>().and_then([](int) -> Optional<int> { return 0; }));

  EXPECT_EQ(std::nullopt, Optional<int>().and_then([](int) { return Optional<int>(); }));



  // By value.

  EXPECT_EQ(0, Optional(0).and_then([](int x) { return Optional(x); }));

  EXPECT_EQ(123, Optional("123").and_then(parse_int));

  EXPECT_EQ(std::nullopt, Optional("abc").and_then(parse_int));



  // By reference.

  {

    Optional opt = 'x';

    EXPECT_EQ('z', opt.and_then([](char& c) {

      c = 'y';

      return Optional('z');

    }));



    EXPECT_EQ('y', opt);

  }



  // By rvalue reference.

  {

    std::string out;

    EXPECT_EQ("xyz"s, Optional("abc"s).and_then([&out](std::string&& str) {

      out = std::move(str);

      return Optional("xyz"s);

    }));



    EXPECT_EQ(out, "abc"s);

  }



  // Chaining.

  using StringVector = StaticVector<std::string, 3>;

  EXPECT_EQ(14u, Optional(StaticVector{"-"s, "1"s})

                     .and_then([](StringVector&& v) -> Optional<StringVector> {

                       if (v.push_back("4"s)) return v;

                       return {};

                     })

                     .and_then([](const StringVector& v) -> Optional<std::string> {

                       if (v.full()) return std::accumulate(v.begin(), v.end(), std::string());

                       return {};

                     })

                     .and_then(parse_int)

                     .and_then([](int i) {

                       return i > 0 ? std::nullopt : std::make_optional(static_cast<unsigned>(-i));

                     }));

}



}  // namespace android::test