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Diffstat (limited to 'src/corelib/kernel/qvariant_p.h')
-rw-r--r-- | src/corelib/kernel/qvariant_p.h | 109 |
1 files changed, 109 insertions, 0 deletions
diff --git a/src/corelib/kernel/qvariant_p.h b/src/corelib/kernel/qvariant_p.h new file mode 100644 index 0000000000..d2a7390938 --- /dev/null +++ b/src/corelib/kernel/qvariant_p.h @@ -0,0 +1,109 @@ +// Copyright (C) 2023 The Qt Company Ltd. +// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only + +#ifndef QVARIANT_P_H +#define QVARIANT_P_H + +// +// W A R N I N G +// ------------- +// +// This file is not part of the Qt API. It exists purely as an +// implementation detail. This header file may change from version to +// version without notice, or even be removed. +// +// We mean it. +// + +#include "qvariant.h" + +QT_BEGIN_NAMESPACE + +inline auto customConstructSharedImpl(size_t size, size_t align) +{ + struct Deleter { + void operator()(QVariant::PrivateShared *p) const + { QVariant::PrivateShared::free(p); } + }; + + // this is exception-safe + std::unique_ptr<QVariant::PrivateShared, Deleter> ptr; + ptr.reset(QVariant::PrivateShared::create(size, align)); + return ptr; +} + +template <typename F> static QVariant::PrivateShared * +customConstructShared(size_t size, size_t align, F &&construct) +{ + auto ptr = customConstructSharedImpl(size, align); + construct(ptr->data()); + return ptr.release(); +} + +inline int QVariant::PrivateShared::computeOffset(PrivateShared *ps, size_t align) +{ + return int(((quintptr(ps) + sizeof(PrivateShared) + align - 1) & ~(align - 1)) - quintptr(ps)); +} + +inline size_t QVariant::PrivateShared::computeAllocationSize(size_t size, size_t align) +{ + size += sizeof(PrivateShared); + if (align > sizeof(PrivateShared)) { + // The alignment is larger than the alignment we can guarantee for the pointer + // directly following PrivateShared, so we need to allocate some additional + // memory to be able to fit the object into the available memory with suitable + // alignment. + size += align - sizeof(PrivateShared); + } + return size; +} + +inline QVariant::PrivateShared *QVariant::PrivateShared::create(size_t size, size_t align) +{ + size = computeAllocationSize(size, align); + void *data = operator new(size); + auto *ps = new (data) QVariant::PrivateShared(); + ps->offset = computeOffset(ps, align); + return ps; +} + +inline void QVariant::PrivateShared::free(PrivateShared *p) +{ + p->~PrivateShared(); + operator delete(p); +} + +inline QVariant::Private::Private(const QtPrivate::QMetaTypeInterface *iface) noexcept + : is_shared(false), is_null(false), packedType(quintptr(iface) >> 2) +{ + Q_ASSERT((quintptr(iface) & 0x3) == 0); +} + +template <typename T> inline +QVariant::Private::Private(std::piecewise_construct_t, const T &t) + : is_shared(!CanUseInternalSpace<T>), is_null(std::is_same_v<T, std::nullptr_t>) +{ + // confirm noexceptness + static constexpr bool isNothrowQVariantConstructible = noexcept(QVariant(t)); + static constexpr bool isNothrowCopyConstructible = std::is_nothrow_copy_constructible_v<T>; + static constexpr bool isNothrowCopyAssignable = std::is_nothrow_copy_assignable_v<T>; + + const QtPrivate::QMetaTypeInterface *iface = QtPrivate::qMetaTypeInterfaceForType<T>(); + Q_ASSERT((quintptr(iface) & 0x3) == 0); + packedType = quintptr(iface) >> 2; + + if constexpr (CanUseInternalSpace<T>) { + static_assert(isNothrowQVariantConstructible == isNothrowCopyConstructible); + static_assert(isNothrowQVariantConstructible == isNothrowCopyAssignable); + new (data.data) T(t); + } else { + static_assert(!isNothrowQVariantConstructible); // we allocate memory, even if T doesn't + data.shared = customConstructShared(sizeof(T), alignof(T), [=](void *where) { + new (where) T(t); + }); + } +} + +QT_END_NAMESPACE + +#endif // QVARIANT_P_H |