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QDirListing: make end() return a sentinel

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This simplifies the implementation, and is more secure, because you no
longer can compare const_iterator with const_iterator and get a
non-sensical result (unequal, even though copies of each other).

Requires the STL algorithm test to be ported to C++20 ranges, because
classical STL algorithms can't deal with decltype(first) !=
decltype(last).

Found in API-review.

As a drive-by, make the reversed and inverted operators conditional on
!__cpp_impl_three_way_comparison.

Change-Id: Icd0e4dac277bd3b053f7b648f8c3f9d9f3753299
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>
(cherry picked from commit 2569ca0f34fe15a2e5c828b708f1406be8d53836)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
This commit is contained in:
Marc Mutz 2024-09-02 14:48:13 +02:00 committed by Qt Cherry-pick Bot
parent e9a95ae4b8
commit 089263fd4f
3 changed files with 47 additions and 19 deletions
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26
src/corelib/io/qdirlisting.cpp
View File

@ -32,12 +32,16 @@
files, recursively:
\snippet code/src_corelib_io_qdirlisting.cpp 6
Iterators constructed by QDirListing (QDirListing::const_iterator) are
Iterators constructed by QDirListing (QDirListing::const_iterator)
model C++20
\l{https://en.cppreference.com/w/cpp/iterator/input_iterator}{std::input_iterator},
that is, they are
forward-only, single-pass iterators, that don't allow random access. They
can be used in ranged-for loops (or with STL alogrithms that don't
can be used in ranged-for loops (or with C++20 range algorithms that don't
require random access iterators). Dereferencing a valid iterator returns
a QDirListing::DirEntry object. The (c)end() iterator marks the end of
the iteration. Dereferencing the end iterator is undefined behavior.
a QDirListing::DirEntry object. The (c)end() sentinel marks the end of
the iteration. Dereferencing an iterator that is equal to \l{sentinel} is
undefined behavior.
QDirListing::DirEntry offers a subset of QFileInfo's API (for example,
fileName(), filePath(), exists()). Internally, DirEntry only constructs
@ -660,8 +664,8 @@ QStringList QDirListing::nameFilters() const
/*!
\fn QDirListing::const_iterator QDirListing::begin() const
\fn QDirListing::const_iterator QDirListing::cbegin() const
\fn QDirListing::const_iterator QDirListing::end() const
\fn QDirListing::const_iterator QDirListing::cend() const
\fn QDirListing::sentinel QDirListing::end() const
\fn QDirListing::sentinel QDirListing::cend() const
(c)begin() returns a QDirListing::const_iterator that can be used to
iterate over directory entries.
@ -673,8 +677,8 @@ QStringList QDirListing::nameFilters() const
\li Can be used in ranged-for loops; or with STL algorithms that don't
require random access iterators
\li Dereferencing a valid iterator returns a \c{const DirEntry &}
\li (c)end() returns a sentinel-like const_iterator that signals the
end of the iteration. Dereferencing the end() iterator is undefined
\li (c)end() returns a sentinel that signals the end of the iteration.
Dereferencing an iterator that compares equal to end() is undefined
behavior
\li Each time (c)begin() is called on the same QDirListing object,
the internal state is reset and the iteration starts anew
@ -689,6 +693,10 @@ QStringList QDirListing::nameFilters() const
Here's how to find and read all files filtered by name, recursively:
\snippet code/src_corelib_io_qdirlisting.cpp 1
\note The "classical" STL algorithms don't support iterator/sentinel, so
you need to use C++20 std::ranges algorithms fo QDirListing, or else a
3rd-party library that provides range-based algorithms in C++17.
\sa QDirListing::DirEntry
*/
QDirListing::const_iterator QDirListing::begin() const
@ -719,7 +727,7 @@ QDirListing::const_iterator &QDirListing::const_iterator::operator++()
{
dirListPtr->advance();
if (!dirListPtr->hasIterators())
*this = {}; // All done, make `this` the end() iterator
*this = {}; // All done, make `this` equal to the end() iterator
return *this;
}

27
src/corelib/io/qdirlisting.h
View File

@ -94,6 +94,12 @@ public:
Q_CORE_EXPORT QDateTime fileTime(QFileDevice::FileTime type, const QTimeZone &tz) const;
};
class sentinel
{
friend constexpr bool operator==(sentinel, sentinel) noexcept { return true; }
friend constexpr bool operator!=(sentinel, sentinel) noexcept { return false; }
};
class const_iterator
{
friend class QDirListing;
@ -112,23 +118,28 @@ public:
pointer operator->() const { return &dirEntry; }
Q_CORE_EXPORT const_iterator &operator++();
const_iterator operator++(int) { auto tmp = *this; operator++(); return tmp; };
friend bool operator==(const const_iterator &lhs, const const_iterator &rhs) noexcept
friend bool operator==(const const_iterator &lhs, sentinel) noexcept
{
// This is only used for the sentinel end iterator
return lhs.dirListPtr == nullptr && rhs.dirListPtr == nullptr;
return lhs.dirListPtr == nullptr;
}
friend bool operator!=(const const_iterator &lhs, const const_iterator &rhs) noexcept
{ return !(lhs == rhs); }
#ifndef __cpp_impl_three_way_comparison
friend bool operator!=(const const_iterator &lhs, sentinel) noexcept
{ return !operator==(lhs, sentinel{}); }
friend bool operator==(sentinel, const const_iterator &rhs) noexcept
{ return operator==(rhs, sentinel{}); }
friend bool operator!=(sentinel, const const_iterator &rhs) noexcept
{ return !operator==(sentinel{}, rhs); }
#endif // __cpp_impl_three_way_comparison
};
Q_CORE_EXPORT const_iterator begin() const;
const_iterator cbegin() const { return begin(); }
const_iterator end() const { return {}; }
const_iterator cend() const { return end(); }
sentinel end() const { return {}; }
sentinel cend() const { return end(); }
// Qt compatibility
const_iterator constBegin() const { return begin(); }
const_iterator constEnd() const { return end(); }
sentinel constEnd() const { return end(); }
private:
Q_DISABLE_COPY(QDirListing)

13
tests/auto/corelib/io/qdirlisting/tst_qdirlisting.cpp
View File

@ -23,6 +23,8 @@
#include <QStandardPaths>
#endif
#include <algorithm>
using namespace Qt::StringLiterals;
Q_DECLARE_METATYPE(QDirListing::IteratorFlags)
@ -748,18 +750,25 @@ void tst_QDirListing::hiddenDirs()
void tst_QDirListing::withStdAlgorithms()
{
#ifndef __cpp_lib_ranges
QSKIP("This test requires C++20 ranges support enabled in the standard library");
#else
#ifdef __cpp_lib_concepts
static_assert(std::ranges::input_range<QDirListing&>);
#endif
QDirListing dirList(u"entrylist"_s, ItFlag::Recursive);
std::for_each(dirList.cbegin(), dirList.cend(), [](const auto &dirEntry) {
std::ranges::for_each(dirList.cbegin(), dirList.cend(), [](const auto &dirEntry) {
QVERIFY(dirEntry.absoluteFilePath().contains("entrylist"));
});
const auto fileName = "dummy"_L1;
auto it = std::find_if(dirList.cbegin(), dirList.cend(), [fileName](const auto &dirEntry) {
auto it = std::ranges::find_if(dirList.cbegin(), dirList.cend(), [fileName](const auto &dirEntry) {
return dirEntry.fileName() == fileName;
});
QVERIFY(it != dirList.cend());
QCOMPARE(it->fileName(), fileName);
#endif
}
QTEST_MAIN(tst_QDirListing)