gecko-dev/mfbt/tests/TestCompactPair.cpp

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this file,
 * You can obtain one at http://mozilla.org/MPL/2.0/. */

#include <type_traits>

#include "mozilla/Assertions.h"
#include "mozilla/CompactPair.h"

using mozilla::CompactPair;
using mozilla::MakeCompactPair;

// Sizes aren't part of the guaranteed CompactPair interface, but we want to
// verify our attempts at compactness through EBO are moderately functional,
// *somewhere*.
#define INSTANTIATE(T1, T2, name, size)                                        \
  CompactPair<T1, T2> name##_1(T1(0), T2(0));                                  \
  static_assert(sizeof(name##_1.first()) > 0,                                  \
                "first method should work on CompactPair<" #T1 ", " #T2 ">");  \
                                                                               \
  static_assert(sizeof(name##_1.second()) > 0,                                 \
                "second method should work on CompactPair<" #T1 ", " #T2 ">"); \
                                                                               \
  static_assert(sizeof(name##_1) == (size),                                    \
                "CompactPair<" #T1 ", " #T2 "> has an unexpected size");       \
                                                                               \
  CompactPair<T2, T1> name##_2(T2(0), T1(0));                                  \
  static_assert(sizeof(name##_2.first()) > 0,                                  \
                "first method should work on CompactPair<" #T2 ", " #T1 ">");  \
                                                                               \
  static_assert(sizeof(name##_2.second()) > 0,                                 \
                "second method should work on CompactPair<" #T2 ", " #T1 ">"); \
                                                                               \
  static_assert(sizeof(name##_2) == (size),                                    \
                "CompactPair<" #T2 ", " #T1 "> has an unexpected size");

static constexpr std::size_t sizemax(std::size_t a, std::size_t b) {
  return (a > b) ? a : b;
}

INSTANTIATE(int, int, prim1, 2 * sizeof(int));
INSTANTIATE(int, long, prim2,
            sizeof(long) + sizemax(sizeof(int), alignof(long)));

struct EmptyClass {
  explicit EmptyClass(int) {}
};
struct NonEmpty {
  char mC;
  explicit NonEmpty(int) : mC('\0') {}
};

INSTANTIATE(int, EmptyClass, both1, sizeof(int));
INSTANTIATE(int, NonEmpty, both2, sizeof(int) + alignof(int));
INSTANTIATE(EmptyClass, NonEmpty, both3, 1);

struct A {
  char dummy;
  explicit A(int) : dummy('\0') {}
};
struct B : A {
  explicit B(int aI) : A(aI) {}
};

INSTANTIATE(A, A, class1, 2);
INSTANTIATE(A, B, class2, 2);
INSTANTIATE(A, EmptyClass, class3, 1);

struct EmptyNonMovableNonDefaultConstructible {
  explicit EmptyNonMovableNonDefaultConstructible(int) {}

  EmptyNonMovableNonDefaultConstructible(
      const EmptyNonMovableNonDefaultConstructible&) = delete;
  EmptyNonMovableNonDefaultConstructible(
      EmptyNonMovableNonDefaultConstructible&&) = delete;
  EmptyNonMovableNonDefaultConstructible& operator=(
      const EmptyNonMovableNonDefaultConstructible&) = delete;
  EmptyNonMovableNonDefaultConstructible& operator=(
      EmptyNonMovableNonDefaultConstructible&&) = delete;
};

static void TestInPlaceConstruction() {
  constexpr int firstValue = 42;
  constexpr int secondValue = 43;

  {
    const CompactPair<EmptyNonMovableNonDefaultConstructible, int> pair{
        std::piecewise_construct, std::tuple(firstValue),
        std::tuple(secondValue)};
    MOZ_RELEASE_ASSERT(pair.second() == secondValue);
  }

  {
    const CompactPair<int, EmptyNonMovableNonDefaultConstructible> pair{
        std::piecewise_construct, std::tuple(firstValue),
        std::tuple(secondValue)};
    MOZ_RELEASE_ASSERT(pair.first() == firstValue);
  }

  {
    const CompactPair<int, int> pair{std::piecewise_construct,
                                     std::tuple(firstValue),
                                     std::tuple(secondValue)};
    MOZ_RELEASE_ASSERT(pair.first() == firstValue);
    MOZ_RELEASE_ASSERT(pair.second() == secondValue);
  }

  {
    const CompactPair<EmptyNonMovableNonDefaultConstructible,
                      EmptyNonMovableNonDefaultConstructible>
        pair{std::piecewise_construct, std::tuple(firstValue),
             std::tuple(secondValue)};

    // nothing to assert here...
  }
}

struct OtherEmpty : EmptyClass {
  explicit OtherEmpty(int aI) : EmptyClass(aI) {}
};

// C++11 requires distinct objects of the same type, within the same "most
// derived object", to have different addresses.  CompactPair allocates its
// elements as two bases, a base and a member, or two members.  If the two
// elements have non-zero size or are unrelated, no big deal.  But if they're
// both empty and related, something -- possibly both -- must be inflated.
// Exactly which are inflated depends which CompactPairHelper specialization is
// used.  We could potentially assert something about size for this case, but
// whatever we could assert would be very finicky.  Plus it's two empty classes
// -- hardly likely. So don't bother trying to assert anything about this case.
// INSTANTIATE(EmptyClass, OtherEmpty, class4, ...something finicky...);

int main() {
  A a(0);
  B b(0);
  const A constA(0);
  const B constB(0);

  // Check that MakeCompactPair generates CompactPair objects of the correct
  // types.
  static_assert(
      std::is_same_v<decltype(MakeCompactPair(A(0), B(0))), CompactPair<A, B>>,
      "MakeCompactPair should strip rvalue references");
  static_assert(
      std::is_same_v<decltype(MakeCompactPair(a, b)), CompactPair<A, B>>,
      "MakeCompactPair should strip lvalue references");
  static_assert(std::is_same_v<decltype(MakeCompactPair(constA, constB)),
                               CompactPair<A, B>>,
                "MakeCompactPair should strip CV-qualifiers");

  // Check that copy assignment and move assignment work.
  a = constA;
  a = A(0);

  TestInPlaceConstruction();

  return 0;
}