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/****************************************************************************
**
** Copyright (C) 2016 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and The Qt Company. For licensing terms
** and conditions see https://www.qt.io/terms-conditions. For further
** information use the contact form at https://www.qt.io/contact-us.
**
** GNU Free Documentation License Usage
** Alternatively, this file may be used under the terms of the GNU Free
** Documentation License version 1.3 as published by the Free Software
** Foundation and appearing in the file included in the packaging of
** this file. Please review the following information to ensure
** the GNU Free Documentation License version 1.3 requirements
** will be met: https://www.gnu.org/licenses/fdl-1.3.html.
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\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}
*/
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