qflags.qdoc

Go to the documentation of this file.

// Copyright (C) 2022 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
 
/*!
    \class QFlag
    \inmodule QtCore
    \brief The QFlag class is a helper data type for QFlags.
 
    It is equivalent to a plain \c int, except with respect to
    function overloading and type conversions. You should never need
    to use this class in your applications.
 
    \sa QFlags
*/
 
/*!
    \fn QFlag::QFlag(int value)
 
    Constructs a QFlag object that stores the \a value.
*/
 
/*!
    \fn QFlag::QFlag(uint value)
    \since 5.3
 
    Constructs a QFlag object that stores the \a value.
*/
 
/*!
    \fn QFlag::QFlag(short value)
    \since 5.3
 
    Constructs a QFlag object that stores the \a value.
*/
 
/*!
    \fn QFlag::QFlag(ushort value)
    \since 5.3
 
    Constructs a QFlag object that stores the \a value.
*/
 
/*!
    \fn QFlag::operator int() const
 
    Returns the value stored by the QFlag object.
*/
 
/*!
    \fn QFlag::operator uint() const
    \since 5.3
 
    Returns the value stored by the QFlag object.
*/
 
/*!
    \class QFlags
    \inmodule QtCore
    \brief The QFlags class provides a type-safe way of storing
    OR-combinations of enum values.
 
 
    \ingroup tools
 
    QFlags<Enum> is a template class where \a Enum is an enumeration type.
    QFlags is used throughout Qt for storing combinations of enum values.
 
    The traditional C++ approach for storing OR-combinations of enum
    values is to use an \c int or \c uint variable. The inconvenience
    with this approach is that there's no type checking at all; any
    enum value can be OR'd with any other enum value and passed on to
    a function that takes an \c int or \c uint.
 
    Since Qt 6.9, QFlags supports 64-bit enumerations. It is recommended to use
    explicit (fixed) underlying types when going above 32 bits, to ensure
    neither the enumeration nor the QFlags type change sizes if an enumerator
    is removed. Some compilers will also only make the \c enum type larger than
    32 bits with explicit underlying types.
 
    Qt uses QFlags to provide type safety. For example, the
    Qt::Alignment type is simply a typedef for
    QFlags<Qt::AlignmentFlag>. QLabel::setAlignment() takes a
    Qt::Alignment parameter, which means that any combination of
    Qt::AlignmentFlag values, or \c{{ }}, is legal:
 
    \snippet code/src_corelib_global_qglobal_widgets.cpp 0
 
    If you try to pass a value from another enum or just a plain
    integer other than 0, the compiler will report an error. If you
    need to cast integer values to flags in a untyped fashion, you can
    use the explicit QFlags constructor as cast operator.
 
    If you want to use QFlags for your own enum types, use
    the Q_DECLARE_FLAGS() and Q_DECLARE_OPERATORS_FOR_FLAGS().
    In this case Q_DECLARE_FLAGS() must appear in the same scope (class or
    namespace) as the corresponding enum.
 
    Example:
 
    \snippet code/src_corelib_global_qglobal.cpp 1
 
    You can then use the \c MyClass::Options type to store
    combinations of \c MyClass::Option values.
 
    \section1 Flags and the Meta-Object System
 
    The Q_DECLARE_FLAGS() macro does not expose the flags to the meta-object
    system, so they cannot be used by Qt Script or edited in \QD.
    To make the flags available for these purposes, the Q_FLAG() macro must
    be used:
 
    \snippet code/src_corelib_global_qglobal.cpp meta-object flags
 
    \section1 Naming Convention
 
    A sensible naming convention for enum types and associated QFlags
    types is to give a singular name to the enum type (e.g., \c
    Option) and a plural name to the QFlags type (e.g., \c Options).
    When a singular name is desired for the QFlags type (e.g., \c
    Alignment), you can use \c Flag as the suffix for the enum type
    (e.g., \c AlignmentFlag).
*/
 
/*!
    \typedef QFlags::Int
    \since 5.0
 
    Typedef for the integer type used for storage as well as for
    implicit conversion. Either \c qintXX or \c quintXX, depending on
    whether the enum's underlying type is signed or unsigned and, since Qt 6.9,
    the enum's size. Typically, it will be \c qint32 (\c{int}) or \c quint32
    (\c{unsigned}).
*/
 
/*!
    \typedef QFlags::enum_type
 
    Typedef for the Enum template type.
*/
 
/*!
    \fn template<typename Enum> QFlags<Enum>::QFlags(const QFlags &other)
 
    Constructs a copy of \a other.
*/
 
/*!
    \fn template <typename Enum> QFlags<Enum>::QFlags(Enum flags)
 
    Constructs a QFlags object storing the \a flags.
*/
 
/*!
    \fn template <typename Enum> QFlags<Enum>::QFlags()
    \since 5.15
 
    Constructs a QFlags object with no flags set.
*/
 
/*!
    \fn template <typename Enum> QFlags<Enum>::QFlags(QFlag flag)
 
    Constructs a QFlags object initialized with the integer \a flag.
 
    The QFlag type is a helper type. By using it here instead of \c
    int, we effectively ensure that arbitrary enum values cannot be
    cast to a QFlags, whereas untyped enum values (i.e., \c int
    values) can.
 
    This constructor is only present for 32-bit \c Enum types. To support all
    enum sizes, consider the constructor using \c{std::in_place_t}.
*/
 
/*!
    \fn template <typename Enum> QFlags<Enum>::QFlags(std::in_place_t, Int flags)
    \since 6.9
 
    Constructs a QFlags object initialized with the integer \a flags.
*/
 
/*!
    \fn template <typename Enum> QFlags<Enum>::QFlags(std::initializer_list<Enum> flags)
    \since 5.4
 
    Constructs a QFlags object initialized with all \a flags
    combined using the bitwise OR operator.
 
    \sa operator|=(), operator|()
*/
 
/*!
    \fn template <typename Enum> QFlags &QFlags<Enum>::operator=(const QFlags &other)
 
    Assigns \a other to this object and returns a reference to this
    object.
*/
 
/*!
    \fn template <typename Enum> QFlags &QFlags<Enum>::operator&=(int mask)
 
    Performs a bitwise AND operation with \a mask and stores the
    result in this QFlags object. Returns a reference to this object.
 
//! [unsafe-integer]
    This operator is disabled if the \c{QT_TYPESAFE_FLAGS} macro is defined.
    Note that it is not extended to 64-bit for 64-bit QFlags either: for 64-bit
    support, use the type-safe overload.
//! [unsafe-integer]
 
    \sa operator&(), operator|=(), operator^=()
*/
 
/*!
    \fn template <typename Enum> QFlags &QFlags<Enum>::operator&=(uint mask)
 
    \overload
    \include qflags.qdoc unsafe-integer
*/
 
/*!
    \fn template <typename Enum> QFlags &QFlags<Enum>::operator&=(Enum mask)
 
    \overload
*/
 
/*!
    \fn template <typename Enum> QFlags &QFlags<Enum>::operator&=(QFlags mask)
    \since 6.2
 
    \overload
*/
 
/*!
    \fn template <typename Enum> QFlags &QFlags<Enum>::operator|=(QFlags other)
 
    Performs a bitwise OR operation with \a other and stores the
    result in this QFlags object. Returns a reference to this object.
 
    \sa operator|(), operator&=(), operator^=()
*/
 
/*!
    \fn template <typename Enum> QFlags &QFlags<Enum>::operator|=(Enum other)
 
    \overload
*/
 
/*!
    \fn template <typename Enum> QFlags &QFlags<Enum>::operator^=(QFlags other)
 
    Performs a bitwise XOR operation with \a other and stores the
    result in this QFlags object. Returns a reference to this object.
 
    \sa operator^(), operator&=(), operator|=()
*/
 
/*!
    \fn template <typename Enum> QFlags &QFlags<Enum>::operator^=(Enum other)
 
    \overload
*/
 
/*!
    \fn template <typename Enum> QFlags<Enum>::operator Int() const
 
    Returns the value stored in the QFlags object as an integer.
 
    \sa Int
*/
 
/*!
    \fn template <typename Enum> QFlags QFlags<Enum>::operator|(QFlags other) const
 
    Returns a QFlags object containing the result of the bitwise OR
    operation on this object and \a other.
 
    \sa operator|=(), operator^(), operator&(), operator~()
*/
 
/*!
    \fn template <typename Enum> QFlags QFlags<Enum>::operator|(Enum other) const
 
    \overload
*/
 
/*!
    \fn template <typename Enum> QFlags QFlags<Enum>::operator^(QFlags other) const
 
    Returns a QFlags object containing the result of the bitwise XOR
    operation on this object and \a other.
 
    \sa operator^=(), operator&(), operator|(), operator~()
*/
 
/*!
    \fn template <typename Enum> QFlags QFlags<Enum>::operator^(Enum other) const
 
    \overload
*/
 
/*!
    \fn template <typename Enum> QFlags QFlags<Enum>::operator&(int mask) const
 
    Returns a QFlags object containing the result of the bitwise AND
    operation on this object and \a mask.
 
    \include qflags.qdoc unsafe-integer
 
    \sa operator&=(), operator|(), operator^(), operator~()
*/
 
/*!
    \fn template <typename Enum> QFlags QFlags<Enum>::operator&(uint mask) const
 
    \overload
    \include qflags.qdoc unsafe-integer
*/
 
/*!
    \fn template <typename Enum> QFlags QFlags<Enum>::operator&(Enum mask) const
 
    \overload
*/
 
/*!
    \fn template <typename Enum> QFlags QFlags<Enum>::operator&(QFlags mask) const
    \since 6.2
 
    \overload
*/
 
/*!
    \fn template <typename Enum> QFlags QFlags<Enum>::operator~() const
 
    Returns a QFlags object that contains the bitwise negation of
    this object.
 
    \sa operator&(), operator|(), operator^()
*/
 
/*!
    \fn template <typename Enum> bool QFlags<Enum>::operator!() const
 
    Returns \c true if no flag is set (i.e., if the value stored by the
    QFlags object is 0); otherwise returns \c false.
*/
 
/*!
    \fn template <typename Enum> bool QFlags<Enum>::testFlag(Enum flag) const
    \since 4.2
 
    Returns \c true if the flag \a flag is set, otherwise \c false.
 
    \note if \a flag contains multiple bits set to 1 (for instance, if
    it's an enumerator equal to the bitwise-OR of other enumerators)
    then this function will return \c true if and only if all the bits
    are set in this flags object. On the other hand, if \a flag contains
    no bits set to 1 (that is, its value as a integer is 0), then this
    function will return \c true if and only if this flags object also
    has no bits set to 1.
 
    \sa testAnyFlag()
*/
 
/*!
    \fn template <typename Enum> bool QFlags<Enum>::testFlags(QFlags flags) const noexcept
    \since 6.2
 
    Returns \c true if this flags object matches the given \a flags.
 
    If \a flags has any flags set, this flags object matches precisely
    if all flags set in \a flags are also set in this flags object.
    Otherwise, when \a flags has no flags set, this flags object only
    matches if it also has no flags set.
 
    \sa testAnyFlags()
*/
 
/*!
    \fn template <typename Enum> bool QFlags<Enum>::testAnyFlag(Enum flag) const noexcept
    \since 6.2
 
    Returns \c true if \b any flag set in \a flag is also set in this
    flags object, otherwise \c false. If \a flag has no flags set, the
    return will always be \c false.
 
    \sa testFlag()
*/
 
/*!
    \fn template <typename Enum> bool QFlags<Enum>::testAnyFlags(QFlags flags) const noexcept
    \since 6.2
 
    Returns \c true if \b any flag set in \a flags is also set in this
    flags object, otherwise \c false. If \a flags has no flags set, the
    return will always be \c false.
 
    \sa testFlags()
*/
 
/*!
    \fn template <typename Enum> QFlags QFlags<Enum>::setFlag(Enum flag, bool on)
    \since 5.7
 
    Sets the flag \a flag if \a on is \c true or unsets it if
    \a on is \c false. Returns a reference to this object.
*/
 
/*!
    \fn template <typename Enum> QFlags<Enum> QFlags<Enum>::fromInt(Int i) noexcept
    \since 6.2
 
    Constructs a QFlags object representing the integer value \a i.
*/
 
/*!
    \fn template <typename Enum> Int QFlags<Enum>::toInt() const noexcept
    \since 6.2
 
    Returns the value stored in the QFlags object as an integer. Note
    that the returned integer may be signed or unsigned, depending on
    whether the enum's underlying type is signed or unsigned.
 
    \sa Int
*/
 
/*!
    \fn template <typename Enum> size_t qHash(QFlags<Enum> key, size_t seed)
    \since 6.2
    \qhashold{QFlags}
*/
 
/*!
    \fn template <typename Enum> bool QFlags<Enum>::operator==(QFlags<Enum> lhs, QFlags<Enum> rhs)
    \fn template <typename Enum> bool QFlags<Enum>::operator==(QFlags<Enum> lhs, Enum rhs)
    \fn template <typename Enum> bool QFlags<Enum>::operator==(Enum lhs, QFlags<Enum> rhs)
    \since 6.2
 
    Compares \a lhs and \a rhs for equality; the two arguments are
    considered equal if they represent exactly the same value
    (bitmask).
*/
 
/*!
    \fn template <typename Enum> bool QFlags<Enum>::operator!=(QFlags<Enum> lhs, QFlags<Enum> rhs)
    \fn template <typename Enum> bool QFlags<Enum>::operator!=(QFlags<Enum> lhs, Enum rhs)
    \fn template <typename Enum> bool QFlags<Enum>::operator!=(Enum lhs, QFlags<Enum> rhs)
    \since 6.2
 
    Compares \a lhs and \a rhs for inequality; the two arguments are
    considered different if they don't represent exactly the same value
    (bitmask).
*/
 
/*!
    \macro Q_DECLARE_FLAGS(Flags, Enum)
    \relates QFlags
 
    The Q_DECLARE_FLAGS() macro expands to
 
    \snippet code/src_corelib_global_qglobal.cpp 2
 
    \a Enum is the name of an existing enum type, whereas \a Flags is
    the name of the QFlags<\e{Enum}> typedef.
 
    See the QFlags documentation for details.
 
    \sa Q_DECLARE_OPERATORS_FOR_FLAGS()
*/
 
/*!
    \macro Q_DECLARE_OPERATORS_FOR_FLAGS(Flags)
    \relates QFlags
 
    The Q_DECLARE_OPERATORS_FOR_FLAGS() macro declares global
    bitwise operator functions \c operator|(), \c operator&(),
    \c operator^(), \c operator~() and their assignment forms:
    &=, |=, and ^=. for \a Flags, which is of type QFlags<T>.
 
    See the QFlags documentation for details.
 
    \sa Q_DECLARE_FLAGS()
*/