qt-everywhere-src-5.15.1/qtbase/src/corelib/tools/qpair.qdoc

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/*!
    \class QPair
    \inmodule QtCore
    \reentrant
    \brief The QPair class is a template class that stores a pair of items.

    \ingroup tools

    QPair\<T1, T2\> can be used in your application if the STL \c
    pair type is not available. It stores one value of type T1 and
    one value of type T2. It can be used as a return value for a
    function that needs to return two values, or as the value type of
    a \l{Container classes}{generic container}.

    Here's an example of a QPair that stores one QString and one \c
    double value:

    \snippet code/doc_src_qpair.cpp 0

    The components are accessible as public data members called \l
    first and \l second. For example:

    \snippet code/doc_src_qpair.cpp 1

    Note, however, that it is almost always preferable to define a small struct
    to hold the result of a function with multiple return values. A struct
    trivially generalizes to more than two values, and allows more descriptive
    member names than \c{first} and \c{second}:

    \snippet code/doc_src_qpair.cpp struct

    The advent of C++11 automatic variable type deduction (\c{auto}) shifts the
    emphasis from the type name to the name of functions and members. Thus, QPair,
    like \c{std::pair} and \c{std::tuple}, is mostly useful in generic (template)
    code, where defining a dedicated type is not possible.

    QPair's template data types (T1 and T2) must be \l{assignable
    data types}. You cannot, for example, store a QWidget as a value;
    instead, store a QWidget *. A few functions have additional
    requirements; these requirements are documented on a per-function
    basis.

    \sa {Container Classes}
*/

/*! \typedef QPair::first_type

    The type of the first element in the pair (T1).

    \sa first
*/

/*! \typedef QPair::second_type

    The type of the second element in the pair (T2).

    \sa second
*/

/*! \variable QPair::first

    The first element in the pair.
*/

/*! \variable QPair::second

    The second element in the pair.
*/

/*! \fn template <class T1, class T2> QPair<T1, T2>::QPair()

    Constructs an empty pair. The \c first and \c second elements are
    initialized with \l{default-constructed value}s.
*/

/*!
    \fn template <class T1, class T2> QPair<T1, T2>::QPair(const T1 &value1, const T2 &value2)

    Constructs a pair and initializes the \c first element with \a
    value1 and the \c second element with \a value2.

    \sa qMakePair()
*/

/*!
\fn template <class T1, class T2> void QPair<T1, T2>::swap(QPair &other)

    \since 5.5
    Swaps this pair with \a other.

    Equivalent to
    \code
        qSwap(this->first, other.first);
        qSwap(this->second, other.second);
    \endcode

    Swap overloads are found in namespace \c std as well as via
    argument-dependent lookup (ADL) in the namespace of \c{T} .
*/

/*!
\fn template <class T1, class T2> void swap(QPair<T1, T2> &lhs, QPair<T1, T2> &rhs)
    \overload
    \relates QPair
    \since 5.5

    Swaps \a lhs with \a rhs.
*/

/*!
    \fn template <class T1, class T2> template <typename TT1, typename TT2> QPair<T1, T2>::QPair(const QPair<TT1, TT2> &p)
    \since 5.2

    Constructs a pair from the other pair \a p, of types TT1 and TT2. This
    constructor will fail if \c first cannot be initialized from \c p.first or
    if \c second cannot be initialized from \c p.second.

    \sa qMakePair()
*/

/*!
    \fn template <class T1, class T2> template <typename TT1, typename TT2> QPair<T1, T2>::QPair(QPair<TT1, TT2> &&p)
    \since 5.2

    Move-constructs a QPair instance, making it point to the same object that \a p was pointing to.
*/

/*!
    \fn template <class T1, class T2> template <typename TT1, typename TT2> QPair & QPair<T1, T2>::operator=(const QPair<TT1, TT2> &p)
    \since 5.2

    Copies pair \a p into this pair.

    \sa qMakePair()
*/

/*!
    \fn template <class T1, class T2> template <typename TT1, typename TT2> QPair & QPair<T1, T2>::operator=(QPair<TT1, TT2> &&p)
    \since 5.2

    Move-assigns pair \a p into this pair instance.
*/

/*! \fn template <class T1, class T2> bool operator==(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)

    \relates QPair

    Returns \c true if \a p1 is equal to \a p2; otherwise returns \c false.
    Two pairs compare equal if their \c first data members compare
    equal and if their \c second data members compare equal.

    This function requires the T1 and T2 types to have an
    implementation of \c operator==().
*/

/*! \fn template <class T1, class T2> bool operator!=(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)

    \relates QPair

    Returns \c true if \a p1 is not equal to \a p2; otherwise returns
    false. Two pairs compare as not equal if their \c first data
    members are not equal or if their \c second data members are not
    equal.

    This function requires the T1 and T2 types to have an
    implementation of \c operator==().
*/

/*! \fn template <class T1, class T2> bool operator<(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)

    \relates QPair

    Returns \c true if \a p1 is less than \a p2; otherwise returns
    false. The comparison is done on the \c first members of \a p1
    and \a p2; if they compare equal, the \c second members are
    compared to break the tie.

    This function requires the T1 and T2 types to have an
    implementation of \c operator<().
*/

/*! \fn template <class T1, class T2> bool operator>(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)

    \relates QPair

    Returns \c true if \a p1 is greater than \a p2; otherwise returns
    false. The comparison is done on the \c first members of \a p1
    and \a p2; if they compare equal, the \c second members are
    compared to break the tie.

    This function requires the T1 and T2 types to have an
    implementation of \c operator<().
*/

/*! \fn template <class T1, class T2> bool operator<=(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)

    \relates QPair

    Returns \c true if \a p1 is less than or equal to \a p2; otherwise
    returns \c false. The comparison is done on the \c first members of
    \a p1 and \a p2; if they compare equal, the \c second members are
    compared to break the tie.

    This function requires the T1 and T2 types to have an
    implementation of \c operator<().
*/

/*! \fn template <class T1, class T2> bool operator>=(const QPair<T1, T2> &p1, const QPair<T1, T2> &p2)

    \relates QPair

    Returns \c true if \a p1 is greater than or equal to \a p2;
    otherwise returns \c false. The comparison is done on the \c first
    members of \a p1 and \a p2; if they compare equal, the \c second
    members are compared to break the tie.

    This function requires the T1 and T2 types to have an
    implementation of \c operator<().
*/

/*!
    \fn template <class T1, class T2> QPair<T1, T2> qMakePair(const T1 &value1, const T2 &value2)

    \relates QPair

    Returns a QPair\<T1, T2\> that contains \a value1 and \a value2.
    Example:

    \snippet code/doc_src_qpair.cpp 2

    This is equivalent to QPair<T1, T2>(\a value1, \a value2), but
    usually requires less typing.
*/

/*! \fn template <class T1, class T2> QDataStream &operator>>(QDataStream &in, QPair<T1, T2> &pair)

    \relates QPair

    Reads a pair from stream \a in into \a pair.

    This function requires the T1 and T2 types to implement \c operator>>().

    \sa {Serializing Qt Data Types}
*/

/*! \fn template <class T1, class T2> QDataStream &operator<<(QDataStream &out, const QPair<T1, T2> &pair)

    \relates QPair

    Writes the pair \a pair to stream \a out.

    This function requires the T1 and T2 types to implement \c operator<<().

    \sa {Serializing Qt Data Types}
*/