VectorTraits.h

/*
 * Copyright (C) 2006, 2007, 2008 Apple Inc. All rights reserved.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public License
 * along with this library; see the file COPYING.LIB.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
 * Boston, MA 02110-1301, USA.
 *
 */

#ifndef WTF_VectorTraits_h
#define WTF_VectorTraits_h

#include "wtf/RefPtr.h"
#include "wtf/TypeTraits.h"
#include <memory>
#include <type_traits>
#include <utility>

namespace WTF {

template <typename T>
struct VectorTraitsBase {
  static const bool needsDestruction = !IsTriviallyDestructible<T>::value;

  static const bool canInitializeWithMemset =
      IsTriviallyDefaultConstructible<T>::value;
  // true iff memset(slot, 0, size) constructs an unused slot value that is
  // valid for Oilpan to trace and if the value needs destruction, its
  // destructor can be invoked over. The zero'ed value representing an unused
  // slot in the vector's backing storage; it does not have to be equal to
  // what its constructor(s) would create, only be valid for those two uses.
  static const bool canClearUnusedSlotsWithMemset =
      IsTriviallyDefaultConstructible<T>::value;

  static const bool canMoveWithMemcpy = IsTriviallyMoveAssignable<T>::value;
  static const bool canCopyWithMemcpy = IsTriviallyCopyAssignable<T>::value;
  static const bool canFillWithMemset =
      IsTriviallyDefaultConstructible<T>::value && (sizeof(T) == sizeof(char));
  static const bool canCompareWithMemcmp =
      std::is_scalar<T>::value;  // Types without padding.

  // Supports swapping elements using regular std::swap semantics.
  static const bool canSwapUsingCopyOrMove = true;

  template <typename U = void>
  struct IsTraceableInCollection {
    static const bool value = IsTraceable<T>::value;
  };
  // We don't support weak handling in vectors.
  static const WeakHandlingFlag weakHandlingFlag = NoWeakHandlingInCollections;
};

template <typename T>
struct VectorTraits : VectorTraitsBase<T> {};

// Classes marked with SimpleVectorTraits will use memmov, memcpy, memcmp
// instead of constructors, copy operators, etc for initialization, move and
// comparison.
template <typename T>
struct SimpleClassVectorTraits : VectorTraitsBase<T> {
  static const bool canInitializeWithMemset = true;
  static const bool canClearUnusedSlotsWithMemset = true;
  static const bool canMoveWithMemcpy = true;
  static const bool canCompareWithMemcmp = true;
};

// We know std::unique_ptr and RefPtr are simple enough that initializing to 0
// and moving with memcpy (and then not destructing the original) will totally
// work.
template <typename P>
struct VectorTraits<RefPtr<P>> : SimpleClassVectorTraits<RefPtr<P>> {};

template <typename P>
struct VectorTraits<std::unique_ptr<P>>
    : SimpleClassVectorTraits<std::unique_ptr<P>> {
  // std::unique_ptr -> std::unique_ptr has a very particular structure that
  // tricks the normal type traits into thinking that the class is "trivially
  // copyable".
  static const bool canCopyWithMemcpy = false;
};
static_assert(VectorTraits<RefPtr<int>>::canInitializeWithMemset,
              "inefficient RefPtr Vector");
static_assert(VectorTraits<RefPtr<int>>::canMoveWithMemcpy,
              "inefficient RefPtr Vector");
static_assert(VectorTraits<RefPtr<int>>::canCompareWithMemcmp,
              "inefficient RefPtr Vector");
static_assert(VectorTraits<std::unique_ptr<int>>::canInitializeWithMemset,
              "inefficient std::unique_ptr Vector");
static_assert(VectorTraits<std::unique_ptr<int>>::canMoveWithMemcpy,
              "inefficient std::unique_ptr Vector");
static_assert(VectorTraits<std::unique_ptr<int>>::canCompareWithMemcmp,
              "inefficient std::unique_ptr Vector");

template <typename First, typename Second>
struct VectorTraits<std::pair<First, Second>> {
  typedef VectorTraits<First> FirstTraits;
  typedef VectorTraits<Second> SecondTraits;

  static const bool needsDestruction =
      FirstTraits::needsDestruction || SecondTraits::needsDestruction;
  static const bool canInitializeWithMemset =
      FirstTraits::canInitializeWithMemset &&
      SecondTraits::canInitializeWithMemset;
  static const bool canMoveWithMemcpy =
      FirstTraits::canMoveWithMemcpy && SecondTraits::canMoveWithMemcpy;
  static const bool canCopyWithMemcpy =
      FirstTraits::canCopyWithMemcpy && SecondTraits::canCopyWithMemcpy;
  static const bool canFillWithMemset = false;
  static const bool canCompareWithMemcmp =
      FirstTraits::canCompareWithMemcmp && SecondTraits::canCompareWithMemcmp;
  static const bool canClearUnusedSlotsWithMemset =
      FirstTraits::canClearUnusedSlotsWithMemset &&
      SecondTraits::canClearUnusedSlotsWithMemset;
  // Supports swapping elements using regular std::swap semantics.
  static const bool canSwapUsingCopyOrMove = true;
  template <typename U = void>
  struct IsTraceableInCollection {
    static const bool value =
        IsTraceableInCollectionTrait<FirstTraits>::value ||
        IsTraceableInCollectionTrait<SecondTraits>::value;
  };
  // We don't support weak handling in vectors.
  static const WeakHandlingFlag weakHandlingFlag = NoWeakHandlingInCollections;
};

}  // namespace WTF

#define WTF_ALLOW_MOVE_INIT_AND_COMPARE_WITH_MEM_FUNCTIONS(ClassName)     \
  namespace WTF {                                                         \
  static_assert(!IsTriviallyDefaultConstructible<ClassName>::value ||     \
                    !IsTriviallyMoveAssignable<ClassName>::value ||       \
                    !std::is_scalar<ClassName>::value,                    \
                "macro not needed");                                      \
  template <>                                                             \
  struct VectorTraits<ClassName> : SimpleClassVectorTraits<ClassName> {}; \
  }

#define WTF_ALLOW_MOVE_AND_INIT_WITH_MEM_FUNCTIONS(ClassName)         \
  namespace WTF {                                                     \
  static_assert(!IsTriviallyDefaultConstructible<ClassName>::value || \
                    !IsTriviallyMoveAssignable<ClassName>::value,     \
                "macro not needed");                                  \
  template <>                                                         \
  struct VectorTraits<ClassName> : VectorTraitsBase<ClassName> {      \
    static const bool canInitializeWithMemset = true;                 \
    static const bool canClearUnusedSlotsWithMemset = true;           \
    static const bool canMoveWithMemcpy = true;                       \
  };                                                                  \
  }

#define WTF_ALLOW_INIT_WITH_MEM_FUNCTIONS(ClassName)                \
  namespace WTF {                                                   \
  static_assert(!IsTriviallyDefaultConstructible<ClassName>::value, \
                "macro not needed");                                \
  template <>                                                       \
  struct VectorTraits<ClassName> : VectorTraitsBase<ClassName> {    \
    static const bool canInitializeWithMemset = true;               \
    static const bool canClearUnusedSlotsWithMemset = true;         \
  };                                                                \
  }

#define WTF_ALLOW_CLEAR_UNUSED_SLOTS_WITH_MEM_FUNCTIONS(ClassName)  \
  namespace WTF {                                                   \
  static_assert(!IsTriviallyDefaultConstructible<ClassName>::value, \
                "macro not needed");                                \
  template <>                                                       \
  struct VectorTraits<ClassName> : VectorTraitsBase<ClassName> {    \
    static const bool canClearUnusedSlotsWithMemset = true;         \
  };                                                                \
  }

using WTF::VectorTraits;
using WTF::SimpleClassVectorTraits;

#endif  // WTF_VectorTraits_h