qtypeinfo.qdoc

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// Copyright (C) 2022 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
 
/*!
    \macro Q_DECLARE_TYPEINFO(Type, Flags)
    \relates <QTypeInfo>
 
    You can use this macro to specify information about a custom type
    \a Type. With accurate type information, Qt's \l{Container Classes}
    {generic containers} can choose appropriate storage methods and
    algorithms.
 
    \a Flags can be one of the following:
 
    \list
    \li \c Q_PRIMITIVE_TYPE specifies that \a Type can be created by
        zero-initializing its storage, requires no operation to be properly
        destroyed, and for which memcpy()ing creates a valid independent
        copy of the object.
    \li \c Q_RELOCATABLE_TYPE specifies that \a Type has a constructor
       and/or a destructor but can be moved in memory using \c
       memcpy().
    \li \c Q_MOVABLE_TYPE is the same as \c Q_RELOCATABLE_TYPE. Prefer to use
        \c Q_RELOCATABLE_TYPE in new code. Note: despite the name, this
        has nothing to do with move constructors or C++ move semantics.
    \li \c Q_COMPLEX_TYPE (the default) specifies that \a Type has
       constructors and/or a destructor and that it may not be moved
       in memory.
    \endlist
 
    Example of a "primitive" type:
 
    \snippet code/src_corelib_global_qglobal.cpp 38
 
    An example of a non-POD "primitive" type is QUuid: Even though
    QUuid has constructors (and therefore isn't POD), every bit
    pattern still represents a valid object, and memcpy() can be used
    to create a valid independent copy of a QUuid object.
 
    Example of a relocatable type:
 
    \snippet code/src_corelib_global_qglobal.cpp 39
 
    Qt will try to detect the class of a type using
    \l {https://en.cppreference.com/w/cpp/types/is_trivial} {std::is_trivial_v<T>}
    to identify primitive
    types and it will require both
    \l {https://en.cppreference.com/w/cpp/types/is_trivially_copyable} {std::is_trivially_copyable_v<T>}
    and
    \l {https://en.cppreference.com/w/cpp/types/is_destructible} {std::is_trivially_destructible_v<T>}
    to identify relocatable types.
    Use this macro to tune the behavior.
    For instance many types would be candidates for Q_RELOCATABLE_TYPE despite
    not being trivially-copyable.
*/