pw_result/expected_test.cc

// Copyright 2023 The Pigweed Authors
//
// 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.

#include "pw_result/expected.h"

#include "gtest/gtest.h"

namespace pw {
namespace {

struct Defaults {
  Defaults() = default;
  Defaults(const Defaults&) = default;
  Defaults(Defaults&&) = default;
  Defaults& operator=(const Defaults&) = default;
  Defaults& operator=(Defaults&&) = default;
};

struct NoDefaultConstructor {
  NoDefaultConstructor() = delete;
  NoDefaultConstructor(std::nullptr_t) {}
};

struct NoCopy {
  NoCopy(const NoCopy&) = delete;
  NoCopy(NoCopy&&) = default;
  NoCopy& operator=(const NoCopy&) = delete;
  NoCopy& operator=(NoCopy&&) = default;
};

struct NoCopyNoMove {
  NoCopyNoMove(const NoCopyNoMove&) = delete;
  NoCopyNoMove(NoCopyNoMove&&) = delete;
  NoCopyNoMove& operator=(const NoCopyNoMove&) = delete;
  NoCopyNoMove& operator=(NoCopyNoMove&&) = delete;
};

struct NonTrivialDestructor {
  ~NonTrivialDestructor() {}
};

namespace test_constexpr {
// Expected and unexpected are constexpr types.
constexpr expected<int, int> kExpectedConstexpr1;
constexpr expected<int, int> kExpectedConstexpr2{5};
constexpr expected<int, int> kExpectedConstexpr3 = unexpected<int>(42);
constexpr unexpected<int> kExpectedConstexprUnexpected{50};
static_assert(kExpectedConstexpr1.has_value());
static_assert(kExpectedConstexpr1.value() == 0);
static_assert(kExpectedConstexpr2.has_value());
static_assert(kExpectedConstexpr2.value() == 5);
static_assert(!kExpectedConstexpr3.has_value());
static_assert(kExpectedConstexpr3.error() == 42);
static_assert(kExpectedConstexprUnexpected.error() == 50);
}  // namespace test_constexpr

namespace test_default_construction {
// Default constructible if and only if T is default constructible.
static_assert(
    std::is_default_constructible<expected<Defaults, Defaults>>::value);
static_assert(!std::is_default_constructible<
              expected<NoDefaultConstructor, Defaults>>::value);
static_assert(std::is_default_constructible<
              expected<Defaults, NoDefaultConstructor>>::value);
static_assert(!std::is_default_constructible<
              expected<NoDefaultConstructor, NoDefaultConstructor>>::value);
// Never default constructible.
static_assert(!std::is_default_constructible<unexpected<Defaults>>::value);
static_assert(
    !std::is_default_constructible<unexpected<NoDefaultConstructor>>::value);
}  // namespace test_default_construction

namespace test_copy_construction {
// Copy constructible if and only if both types are copy constructible.
static_assert(std::is_copy_constructible<expected<Defaults, Defaults>>::value);
static_assert(!std::is_copy_constructible<expected<Defaults, NoCopy>>::value);
static_assert(!std::is_copy_constructible<expected<NoCopy, Defaults>>::value);
static_assert(!std::is_copy_constructible<expected<NoCopy, NoCopy>>::value);
// Copy constructible if and only if E is copy constructible.
static_assert(std::is_copy_constructible<unexpected<Defaults>>::value);
static_assert(!std::is_copy_constructible<unexpected<NoCopy>>::value);
}  // namespace test_copy_construction

namespace test_copy_assignment {
// Copy assignable if and only if both types are copy assignable.
static_assert(std::is_copy_assignable<expected<Defaults, Defaults>>::value);
static_assert(!std::is_copy_assignable<expected<Defaults, NoCopy>>::value);
static_assert(!std::is_copy_assignable<expected<NoCopy, Defaults>>::value);
static_assert(!std::is_copy_assignable<expected<NoCopy, NoCopy>>::value);
// Copy assignable if and only if E is copy assignable.
static_assert(std::is_copy_assignable<unexpected<Defaults>>::value);
static_assert(!std::is_copy_assignable<unexpected<NoCopy>>::value);
}  // namespace test_copy_assignment

namespace test_move_construction {
// Move constructible if and only if both types are move constructible.
static_assert(std::is_move_constructible<expected<Defaults, Defaults>>::value);
static_assert(
    !std::is_move_constructible<expected<Defaults, NoCopyNoMove>>::value);
static_assert(
    !std::is_move_constructible<expected<NoCopyNoMove, Defaults>>::value);
static_assert(
    !std::is_move_constructible<expected<NoCopyNoMove, NoCopyNoMove>>::value);
// Move constructible if and only if E is move constructible.
static_assert(std::is_move_constructible<unexpected<Defaults>>::value);
static_assert(!std::is_move_constructible<unexpected<NoCopyNoMove>>::value);
}  // namespace test_move_construction

namespace test_move_assignment {
// Move assignable if and only if both types are move assignable.
static_assert(std::is_move_assignable<expected<Defaults, Defaults>>::value);
static_assert(
    !std::is_move_assignable<expected<Defaults, NoCopyNoMove>>::value);
static_assert(
    !std::is_move_assignable<expected<NoCopyNoMove, Defaults>>::value);
static_assert(
    !std::is_move_assignable<expected<NoCopyNoMove, NoCopyNoMove>>::value);
// Move assignable if and only if E is move assignable.
static_assert(std::is_move_assignable<unexpected<Defaults>>::value);
static_assert(!std::is_move_assignable<unexpected<NoCopyNoMove>>::value);
}  // namespace test_move_assignment

namespace test_trivial_destructor {
// Destructor is trivial if and only if both types are trivially destructible.
static_assert(
    std::is_trivially_destructible<expected<Defaults, Defaults>>::value);
static_assert(!std::is_trivially_destructible<
              expected<NonTrivialDestructor, Defaults>>::value);
static_assert(!std::is_trivially_destructible<
              expected<Defaults, NonTrivialDestructor>>::value);
static_assert(!std::is_trivially_destructible<
              expected<NonTrivialDestructor, NonTrivialDestructor>>::value);
// Destructor is trivial if and only if E is trivially destructible.
static_assert(std::is_trivially_destructible<unexpected<Defaults>>::value);
static_assert(
    !std::is_trivially_destructible<unexpected<NonTrivialDestructor>>::value);
}  // namespace test_trivial_destructor

expected<int, const char*> FailableFunction1(bool fail, int num) {
  if (fail) {
    return unexpected<const char*>("FailableFunction1");
  }
  return num;
}

expected<std::string, const char*> FailableFunction2(bool fail, int num) {
  if (fail) {
    return unexpected<const char*>("FailableFunction2");
  }
  return std::to_string(num);
}

expected<int, const char*> FailOnOdd(int x) {
  if (x % 2) {
    return unexpected<const char*>("odd");
  }
  return x;
}

expected<std::string, const char*> ItoaFailOnNegative(int x) {
  if (x < 0) {
    return unexpected<const char*>("negative");
  }
  return std::to_string(x);
}

expected<char, const char*> GetSecondChar(const std::string& s) {
  if (s.size() < 2) {
    return unexpected<const char*>("string too small");
  }
  return s[1];
}

int Decrement(int x) { return x - 1; }

template <class T, class E>
expected<void, E> Consume(const expected<T, E>& e) {
  return e.transform([](auto) {});
}

TEST(ExpectedTest, HoldIntValueSuccess) {
  auto x = FailableFunction1(false, 10);
  ASSERT_TRUE(x.has_value());
  EXPECT_EQ(x.value(), 10);
  EXPECT_EQ(*x, 10);
  EXPECT_EQ(x.value_or(33), 10);
  EXPECT_EQ(x.error_or("no error"), std::string("no error"));
}

TEST(ExpectedTest, HoldIntValueFail) {
  auto x = FailableFunction1(true, 10);
  ASSERT_FALSE(x.has_value());
  EXPECT_EQ(x.error(), std::string("FailableFunction1"));
  EXPECT_EQ(x.value_or(33), 33);
  EXPECT_EQ(x.error_or("no error"), std::string("FailableFunction1"));
}

TEST(ExpectedTest, HoldStringValueSuccess) {
  auto x = FailableFunction2(false, 42);
  ASSERT_TRUE(x.has_value());
  EXPECT_EQ(x.value(), std::string("42"));
  EXPECT_EQ(*x, std::string("42"));
  EXPECT_EQ(x.value_or("33"), std::string("42"));
  EXPECT_EQ(x.error_or("no error"), std::string("no error"));
}

TEST(ExpectedTest, HoldStringValueFail) {
  auto x = FailableFunction2(true, 42);
  ASSERT_FALSE(x.has_value());
  EXPECT_EQ(x.error(), std::string("FailableFunction2"));
  EXPECT_EQ(x.value_or("33"), std::string("33"));
  EXPECT_EQ(x.error_or("no error"), std::string("FailableFunction2"));
}

TEST(ExpectedTest, MonadicOperation) {
  auto f = [](expected<int, const char*> value) {
    return value.and_then(FailOnOdd)
        .transform(Decrement)
        .transform(Decrement)
        .and_then(ItoaFailOnNegative)
        .and_then(GetSecondChar);
  };
  EXPECT_EQ(f(26).value_or(0), '4');
  EXPECT_EQ(f(26).error_or(nullptr), nullptr);
  EXPECT_EQ(f(25).value_or(0), 0);
  EXPECT_EQ(f(25).error_or(nullptr), std::string("odd"));
  EXPECT_EQ(f(0).value_or(0), 0);
  EXPECT_EQ(f(0).error_or(nullptr), std::string("negative"));
  EXPECT_EQ(f(4).value_or(0), 0);
  EXPECT_EQ(f(4).error_or(nullptr), std::string("string too small"));
  EXPECT_TRUE(Consume(f(26)).has_value());
  EXPECT_EQ(Consume(f(25)).error_or(nullptr), std::string("odd"));
  EXPECT_EQ(Consume(f(0)).error_or(nullptr), std::string("negative"));
  EXPECT_EQ(Consume(f(4)).error_or(nullptr), std::string("string too small"));
}

}  // namespace
}  // namespace pw