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Diffstat (limited to 'src/corelib/tools/qstringview.cpp')
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diff --git a/src/corelib/tools/qstringview.cpp b/src/corelib/tools/qstringview.cpp new file mode 100644 index 0000000000..8504b941b3 --- /dev/null +++ b/src/corelib/tools/qstringview.cpp @@ -0,0 +1,533 @@ +/**************************************************************************** +** +** Copyright (C) 2017 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Marc Mutz <marc.mutz@kdab.com> +** Contact: http://www.qt.io/licensing/ +** +** This file is part of the QtCore module of the Qt Toolkit. +** +** $QT_BEGIN_LICENSE:LGPL$ +** 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 Lesser General Public License Usage +** Alternatively, this file may be used under the terms of the GNU Lesser +** General Public License version 3 as published by the Free Software +** Foundation and appearing in the file LICENSE.LGPL3 included in the +** packaging of this file. Please review the following information to +** ensure the GNU Lesser General Public License version 3 requirements +** will be met: https://www.gnu.org/licenses/lgpl-3.0.html. +** +** GNU General Public License Usage +** Alternatively, this file may be used under the terms of the GNU +** General Public License version 2.0 or (at your option) the GNU General +** Public license version 3 or any later version approved by the KDE Free +** Qt Foundation. The licenses are as published by the Free Software +** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3 +** included in the packaging of this file. Please review the following +** information to ensure the GNU General Public License requirements will +** be met: https://www.gnu.org/licenses/gpl-2.0.html and +** https://www.gnu.org/licenses/gpl-3.0.html. +** +** $QT_END_LICENSE$ +** +****************************************************************************/ + +#include "qstringview.h" + +QT_BEGIN_NAMESPACE + +/*! + \class QStringView + \inmodule QtCore + \since 5.10 + \brief The QStringView class provides a unified view on UTF-16 strings + \reentrant + \ingroup tools + \ingroup string-processing + + QStringView provides a read-only subset of the QString API. + + A string view explicitly stores a portion of a UTF-16 string it does + not own. It acts as an interface type to all kinds of UTF-16 string, + without the need to construct a QString first. + + The UTF-16 string may be represented as an array (or an array-compatible + data-structure such as QString, + std::basic_string, etc.) of \c QChar, \c ushort, \c char16_t (on compilers that + support C++11 Unicode strings) or (on platforms, such as Windows, + where it is a 16-bit type) \c wchar_t. + + QStringView is designed as an interface type; its main use-case is + as a function parameter type. When QStringViews are used as automatic + variables or data members, care must be taken to ensure that the referenced + string data (for example, owned by a QString) outlives the QStringView on all code paths, + lest the string view ends up referencing deleted data. + + When used as an interface type, QStringView allows a single function to accept + a wide variety of UTF-16 string data sources. One function accepting QStringView + thus replaces three function overloads (taking QString, QStringRef, and + \c{(const QChar*, int)}), while at the same time enabling even more string data + sources to be passed to the function, such as \c{u"Hello World"}, a \c char16_t + string literal. + + QStringViews should be passed by value, not by reference-to-const: + \code + void myfun1(QStringView sv); // preferred + void myfun2(const QStringView &sv); // compiles and works, but slower + \endcode + + If you want to give your users maximum freedom in what strings they can pass + to your function, accompany the QStringView overload with overloads for + + \list + \li \e QChar: this overload can delegate to the QStringView version: + \code + void fun(QChar ch) { fun(QStringView(&ch, 1)); } + \endcode + even though, for technical reasons, QStringView cannot provide a + QChar constructor by itself. + \li \e QString: if you store an unmodified copy of the string and thus would + like to take advantage of QString's implicit sharing. + \li QLatin1String: if you can implement the function without converting the + QLatin1String to UTF-16 first; users expect a function overloaded on + QLatin1String to perform strictly less memory allocations than the + semantically equivalent call of the QStringView version, involving + construction of a QString from the QLatin1String. + \endlist + + QStringView can also be used as the return value of a function. If you call a + function returning QStringView, take extra care to not keep the QStringView + around longer than the function promises to keep the referenced string data alive. + If in doubt, obtain a strong reference to the data by calling toString() to convert + the QStringView into a QString. + + QStringView is a \e{Literal Type}. + + \note We strongly discourage the use of QList<QStringView>, + because QList is a very inefficient container for QStringViews (it would heap-allocate + every element). Use QVector (or std::vector) to hold QStringViews instead. + + \sa QString, QStringRef +*/ + +/*! + \typedef QStringView::value_type + + Alias for \c{const QChar}. Provided for compatibility with the STL. +*/ + +/*! + \typedef QStringView::difference_type + + Alias for \c{std::ptrdiff_t}. Provided for compatibility with the STL. +*/ + +/*! + \typedef QStringView::size_type + + Alias for \c{std::ptrdiff_t}. Provided for compatibility with the STL. + + Unlike other Qt classes, QStringView uses \c ptrdiff_t as its \c size_type, to allow + accepting data from \c{std::basic_string} without truncation. The Qt API functions, + for example length(), return \c int, while the STL-compatible functions, for example + size(), return \c size_type. +*/ + +/*! + \typedef QStringView::reference + + Alias for \c{value_type &}. Provided for compatibility with the STL. + + QStringView does not support mutable references, so this is the same + as const_reference. +*/ + +/*! + \typedef QStringView::const_reference + + Alias for \c{value_type &}. Provided for compatibility with the STL. +*/ + +/*! + \typedef QStringView::pointer + + Alias for \c{value_type *}. Provided for compatibility with the STL. + + QStringView does not support mutable pointers, so this is the same + as const_pointer. +*/ + +/*! + \typedef QStringView::const_pointer + + Alias for \c{value_type *}. Provided for compatibility with the STL. +*/ + +/*! + \typedef QStringView::iterator + + This typedef provides an STL-style const iterator for QStringView. + + QStringView does not support mutable iterators, so this is the same + as const_iterator. + + \sa const_iterator, reverse_iterator +*/ + +/*! + \typedef QStringView::const_iterator + + This typedef provides an STL-style const iterator for QStringView. + + \sa iterator, const_reverse_iterator +*/ + +/*! + \typedef QStringView::reverse_iterator + + This typedef provides an STL-style const reverse iterator for QStringView. + + QStringView does not support mutable reverse iterators, so this is the + same as const_reverse_iterator. + + \sa const_reverse_iterator, iterator +*/ + +/*! + \typedef QStringView::const_reverse_iterator + + This typedef provides an STL-style const reverse iterator for QStringView. + + \sa reverse_iterator, const_iterator +*/ + +/*! + \fn QStringView::QStringView() + + Constructs a null string view. + + \sa isNull() +*/ + +/*! + \fn QStringView::QStringView(std::nullptr_t) + + Constructs a null string view. + + \sa isNull() +*/ + +/*! + \fn QStringView::QStringView(QString::Null) + \internal + + Constructs a null string view. + + \sa isNull() +*/ + +/*! + \fn QStringView::QStringView(const Char *str, size_type len) + + Constructs a string view on \a str with length \a len. + + The range \c{[str,len)} must remain valid for the lifetime of this string view object. + + Passing \c nullptr as \a str is safe if \a len is 0, too, and results in a null string view. + + The behavior is undefined if \a len is negative or, when positive, if \a str is \c nullptr. + + This constructor only participates in overload resolution if \c Char is a compatible + character type. The compatible character types are: \c QChar, \c ushort, \c char16_t and + (on platforms, such as Windows, where it is a 16-bit type) \c wchar_t. +*/ + +/*! + \fn QStringView::QStringView(const Char *str) + + Constructs a string view on \a str. The length is determined + by scanning for the first \c{char16_t(0)}. + + \a str must remain valid for the lifetime of this string view object. + + Passing \c nullptr as \a str is safe and results in a null string view. + + This constructor only participates in overload resolution if \c Char is a compatible + character type. The compatible character types are: \c QChar, \c ushort, \c char16_t and + (on platforms, such as Windows, where it is a 16-bit type) \c wchar_t. +*/ + +/*! + \fn QStringView::QStringView(const QString &str) + + Constructs a string view on \a str. + + \c{str.data()} must remain valid for the lifetime of this string view object. + + The string view will be null if and only if \c{str.isNull()}. +*/ + +/*! + \fn QStringView::QStringView(const QStringRef &str) + + Constructs a string view on \a str. + + \c{str.data()} must remain valid for the lifetime of this string view object. + + The string view will be null if and only if \c{str.isNull()}. +*/ + +/*! + \fn QStringView::QStringView(const StdBasicString &str) + + Constructs a string view on \a str. The length is taken from \c{str.size()}. + + \c{str.data()} must remain valid for the lifetime of this string view object. + + This constructor only participates in overload resolution if \c StdBasicString is an + instantiation of \c std::basic_string with a compatible character type. The + compatible character types are: \c QChar, \c ushort, \c char16_t and + (on platforms, such as Windows, where it is a 16-bit type) \c wchar_t. + + The string view will be empty if and only if \c{str.empty()}. It is unspecified + whether this constructor can result in a null string view (\c{str.data()} would + have to return \c nullptr for this). + + \sa isNull(), isEmpty() +*/ + +/*! + \fn QString QStringView::toString() const + + Returns a deep copy of this string view's data as a QString. + + The return value will be the null QString if and only if this string view is null. + + \warning QStringView can store strings with more than 2\sup{30} characters + while QString cannot. Calling this function on a string view for which size() + returns a value greater than \c{INT_MAX / 2} constitutes undefined behavior. +*/ + +/*! + \fn const QChar *QStringView::data() const + + Returns a const pointer to the first character in the string. + + \sa begin(), end() +*/ + +/*! + \fn QStringView::const_iterator QStringView::begin() const + + Returns a const \l{STL-style iterators}{STL-style iterator} pointing to the first character in + the string. + + This function is provided for STL compatibility. + + \sa end(), cbegin(), rbegin(), data() +*/ + +/*! + \fn QStringView::const_iterator QStringView::cbegin() const + + Same as begin(). + + This function is provided for STL compatibility. + + \sa cend(), begin(), crbegin(), data() +*/ + +/*! + \fn QStringView::const_iterator QStringView::end() const + + Returns a const \l{STL-style iterators}{STL-style iterator} pointing to the imaginary + character after the last character in the list. + + This function is provided for STL compatibility. + + \sa begin(), cend(), rend() +*/ + +/*! \fn QStringView::const_iterator QStringView::cend() const + + Same as end(). + + This function is provided for STL compatibility. + + \sa cbegin(), end(), crend() +*/ + +/*! + \fn QStringView::const_reverse_iterator QStringView::rbegin() const + + Returns a const \l{STL-style iterators}{STL-style} reverse iterator pointing to the first + character in the string, in reverse order. + + This function is provided for STL compatibility. + + \sa rend(), crbegin(), begin() +*/ + +/*! + \fn QStringView::const_reverse_iterator QStringView::crbegin() const + + Same as rbegin(). + + This function is provided for STL compatibility. + + \sa crend(), rbegin(), cbegin() +*/ + +/*! + \fn QStringView::const_reverse_iterator QStringView::rend() const + + Returns a \l{STL-style iterators}{STL-style} reverse iterator pointing to one past + the last character in the string, in reverse order. + + This function is provided for STL compatibility. + + \sa rbegin(), crend(), end() +*/ + +/*! + \fn QStringView::const_reverse_iterator QStringView::crend() const + + Same as rend(). + + This function is provided for STL compatibility. + + \sa crbegin(), rend(), cend() +*/ + +/*! + \fn bool QStringView::empty() const + + Returns whether this string view is empty - that is, whether \c{size() == 0}. + + This function is provided for STL compatibility. + + \sa isEmpty(), isNull(), size(), length() +*/ + +/*! + \fn bool QStringView::isEmpty() const + + Returns whether this string view is empty - that is, whether \c{size() == 0}. + + This function is provided for compatibility with other Qt containers. + + \sa empty(), isNull(), size(), length() +*/ + +/*! + \fn bool QStringView::isNull() const + + Returns whether this string view is null - that is, whether \c{data() == nullptr}. + + This functions is provided for compatibility with other Qt containers. + + \sa empty(), isEmpty(), size(), length() +*/ + +/*! + \fn QStringView::size_type QStringView::size() const + + Returns the size of this string view, in UTF-16 code points (that is, + surrogate pairs count as two for the purposes of this function, the same + as in QString and QStringRef). + + \sa empty(), isEmpty(), isNull(), length() +*/ + +/*! + \fn int QStringView::length() const + + Same as size(), except returns the result as an \c int. + + This function is provided for compatibility with other Qt containers. + + \warning QStringView can represent strings with more than 2\sup{31} characters. + Calling this function on a string view for which size() returns a value greater + than \c{INT_MAX} constitutes undefined behavior. + + \sa empty(), isEmpty(), isNull(), size() +*/ + +/*! + \fn QChar QStringView::operator[](size_type n) const + + Returns the character at position \a n in this string view. + + The behavior is undefined if \a n is negative or not less than size(). + + \sa at(), front(), back() +*/ + +/*! + \fn QChar QStringView::at(size_type n) const + + Returns the character at position \a n in this string view. + + The behavior is undefined if \a n is negative or not less than size(). + + \sa operator[](), front(), back() +*/ + +/*! + \fn QChar QStringView::front() const + + Returns the first character in the string. Same as first(). + + This function is provided for STL compatibility. + + \warning Calling this function on an empty string view constitutes + undefined behavior. + + \sa back(), first(), last() +*/ + +/*! + \fn QChar QStringView::back() const + + Returns the last character in the string. Same as last(). + + This function is provided for STL compatibility. + + \warning Calling this function on an empty string view constitutes + undefined behavior. + + \sa front(), first(), last() +*/ + +/*! + \fn QChar QStringView::first() const + + Returns the first character in the string. Same as front(). + + This function is provided for compatibility with other Qt containers. + + \warning Calling this function on an empty string view constitutes + undefined behavior. + + \sa front(), back(), last() +*/ + +/*! + \fn QChar QStringView::last() const + + Returns the last character in the string. Same as back(). + + This function is provided for compatibility with other Qt containers. + + \warning Calling this function on an empty string view constitutes + undefined behavior. + + \sa back(), front(), first() +*/ + +QT_END_NAMESPACE |