qcontainertools_impl.h

Go to the documentation of this file.

// Copyright (C) 2018 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Marc Mutz <marc.mutz@kdab.com>
// Copyright (C) 2018 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
// Copyright (C) 2020 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
// Qt-Security score:significant reason:default
 
#if 0
#pragma qt_sync_skip_header_check
#pragma qt_sync_stop_processing
#endif
 
#ifndef QCONTAINERTOOLS_IMPL_H
#define QCONTAINERTOOLS_IMPL_H
 
#include <QtCore/qglobal.h>
#include <QtCore/qtypeinfo.h>
 
#include <QtCore/q20type_traits.h>
#include <QtCore/qxptype_traits.h>
 
#include <cstring>
#include <iterator>
#include <memory>
#include <algorithm>
 
QT_BEGIN_NAMESPACE
 
namespace QtPrivate
{
 
/*!
  \internal
 
  Returns whether \a p is within a range [b, e). In simplest form equivalent to:
  b <= p < e.
*/
template<typename T>
static constexpr bool q_points_into_range(const T *p, const T *b, const T *e)
{
    if (q20::is_constant_evaluated()) {
        for (; b != e; ++b) {
            if (b == p)
                return true;
        }
        return false;
    }
    return !std::less{}(p, b) && std::less{}(p, e);
}
 
/*!
  \internal
 
  Returns whether \a p is within container \a c. In its simplest form equivalent to:
  c.data() <= p < c.data() + c.size()
*/
template <typename C, typename T>
static constexpr bool q_points_into_range(const T &p, const C &c) noexcept
{
    static_assert(std::is_same_v<decltype(std::data(c)), T>);
 
    // std::distance because QArrayDataPointer has a "qsizetype size"
    // member but no size() function
    return q_points_into_range(p, std::data(c),
                               std::data(c) + std::distance(std::begin(c), std::end(c)));
}
 
QT_WARNING_PUSH
QT_WARNING_DISABLE_GCC("-Wmaybe-uninitialized")
 
template <typename T, typename N>
void q_uninitialized_move_if_noexcept_n(T* first, N n, T* out)
{
    if constexpr (std::is_nothrow_move_constructible_v<T> || !std::is_copy_constructible_v<T>)
        std::uninitialized_move_n(first, n, out);
    else
        std::uninitialized_copy_n(first, n, out);
}
 
template <typename T, typename N>
void q_uninitialized_relocate_n(T* first, N n, T* out)
{
    if constexpr (QTypeInfo<T>::isRelocatable) {
        static_assert(std::is_copy_constructible_v<T> || std::is_move_constructible_v<T>,
                      "Refusing to relocate this non-copy/non-move-constructible type.");
        // Even if n == 0, out == nullptr or first == nullptr are UB for memcpy().
        // Negative n shouldn't happen, but the compiler can't see that and might warn about
        // memcpy being called with an out-of-range argument. Since we need to check for n == 0
        // anyway, check for n > 0 instead and assert below.
        if (n > N(0)) {
            std::memcpy(static_cast<void *>(out),
                        static_cast<const void *>(first),
                        n * sizeof(T));
        } else {
            Q_ASSERT(n == N(0));
        }
    } else {
        q_uninitialized_move_if_noexcept_n(first, n, out);
        if constexpr (QTypeInfo<T>::isComplex)
            std::destroy_n(first, n);
    }
}
 
QT_WARNING_POP
 
/*!
    \internal
 
    A wrapper around std::rotate(), with an optimization for
    Q_RELOCATABLE_TYPEs. We omit the return value, as it would be more work to
    compute in the Q_RELOCATABLE_TYPE case and, unlike std::rotate on
    ForwardIterators, callers can compute the result in constant time
    themselves.
*/
template <typename T>
void q_rotate(T *first, T *mid, T *last)
{
    if constexpr (QTypeInfo<T>::isRelocatable) {
        const auto cast = [](T *p) { return reinterpret_cast<uchar*>(p); };
        std::rotate(cast(first), cast(mid), cast(last));
    } else {
        std::rotate(first, mid, last);
    }
}
 
/*!
    \internal
    Copies all elements, except the ones for which \a pred returns \c true, from
    range [first, last), to the uninitialized memory buffer starting at \a out.
 
    It's undefined behavior if \a out points into [first, last).
 
    Returns a pointer one past the last copied element.
 
    If an exception is thrown, all the already copied elements in the destination
    buffer are destroyed.
*/
template <typename T, typename Predicate>
T *q_uninitialized_remove_copy_if(T *first, T *last, T *out, Predicate &pred)
{
    static_assert(std::is_nothrow_destructible_v<T>,
                  "This algorithm requires that T has a non-throwing destructor");
    Q_ASSERT(!q_points_into_range(out, first, last));
 
    T *dest_begin = out;
    QT_TRY {
        while (first != last) {
            if (!pred(*first)) {
                new (std::addressof(*out)) T(*first);
                ++out;
            }
            ++first;
        }
    } QT_CATCH (...) {
        std::destroy(std::reverse_iterator(out), std::reverse_iterator(dest_begin));
        QT_RETHROW;
    }
    return out;
}
 
template<typename iterator, typename N>
void q_relocate_overlap_n_left_move(iterator first, N n, iterator d_first)
{
    // requires: [first, n) is a valid range
    // requires: d_first + n is reachable from d_first
    // requires: iterator is at least a random access iterator
    // requires: value_type(iterator) has a non-throwing destructor
 
    Q_ASSERT(n);
    Q_ASSERT(d_first < first); // only allow moves to the "left"
    using T = typename std::iterator_traits<iterator>::value_type;
 
    // Watches passed iterator. Unless commit() is called, all the elements that
    // the watched iterator passes through are deleted at the end of object
    // lifetime. freeze() could be used to stop watching the passed iterator and
    // remain at current place.
    //
    // requires: the iterator is expected to always point to an invalid object
    //           (to uninitialized memory)
    struct Destructor
    {
        iterator *iter;
        iterator end;
        iterator intermediate;
 
        Destructor(iterator &it) noexcept : iter(std::addressof(it)), end(it) { }
        void commit() noexcept { iter = std::addressof(end); }
        void freeze() noexcept
        {
            intermediate = *iter;
            iter = std::addressof(intermediate);
        }
        ~Destructor() noexcept
        {
            for (const int step = *iter < end ? 1 : -1; *iter != end;) {
                std::advance(*iter, step);
                (*iter)->~T();
            }
        }
    } destroyer(d_first);
 
    const iterator d_last = d_first + n;
    // Note: use pair and explicitly copy iterators from it to prevent
    // accidental reference semantics instead of copy. equivalent to:
    //
    // auto [overlapBegin, overlapEnd] = std::minmax(d_last, first);
    auto pair = std::minmax(d_last, first);
 
    // overlap area between [d_first, d_first + n) and [first, first + n) or an
    // uninitialized memory area between the two ranges
    iterator overlapBegin = pair.first;
    iterator overlapEnd = pair.second;
 
    // move construct elements in uninitialized region
    while (d_first != overlapBegin) {
        // account for std::reverse_iterator, cannot use new(d_first) directly
        new (std::addressof(*d_first)) T(std::move_if_noexcept(*first));
        ++d_first;
        ++first;
    }
 
    // cannot commit but have to stop - there might be an overlap region
    // which we don't want to delete (because it's part of existing data)
    destroyer.freeze();
 
    // move assign elements in overlap region
    while (d_first != d_last) {
        *d_first = std::move_if_noexcept(*first);
        ++d_first;
        ++first;
    }
 
    Q_ASSERT(d_first == destroyer.end + n);
    destroyer.commit(); // can commit here as ~T() below does not throw
 
    while (first != overlapEnd)
        (--first)->~T();
}
 
/*!
  \internal
 
  Relocates a range [first, n) to [d_first, n) taking care of potential memory
  overlaps. This is a generic equivalent of memmove.
 
  If an exception is thrown during the relocation, all the relocated elements
  are destroyed and [first, n) may contain valid but unspecified values,
  including moved-from values (basic exception safety).
*/
template<typename T, typename N>
void q_relocate_overlap_n(T *first, N n, T *d_first)
{
    static_assert(std::is_nothrow_destructible_v<T>,
                  "This algorithm requires that T has a non-throwing destructor");
 
    if (n == N(0) || first == d_first || first == nullptr || d_first == nullptr)
        return;
 
    if constexpr (QTypeInfo<T>::isRelocatable) {
        std::memmove(static_cast<void *>(d_first), static_cast<const void *>(first), n * sizeof(T));
    } else { // generic version has to be used
        if (d_first < first) {
            q_relocate_overlap_n_left_move(first, n, d_first);
        } else { // first < d_first
            auto rfirst = std::make_reverse_iterator(first + n);
            auto rd_first = std::make_reverse_iterator(d_first + n);
            q_relocate_overlap_n_left_move(rfirst, n, rd_first);
        }
    }
}
 
template <typename T>
struct ArrowProxy
{
    T t;
    T *operator->() noexcept { return &t; }
};
 
template <typename Iterator>
using IfIsInputIterator = typename std::enable_if<
    std::is_convertible<typename std::iterator_traits<Iterator>::iterator_category, std::input_iterator_tag>::value,
    bool>::type;
 
template <typename Iterator>
using IfIsForwardIterator = typename std::enable_if<
    std::is_convertible<typename std::iterator_traits<Iterator>::iterator_category, std::forward_iterator_tag>::value,
    bool>::type;
 
template <typename Iterator>
using IfIsNotForwardIterator = typename std::enable_if<
    !std::is_convertible<typename std::iterator_traits<Iterator>::iterator_category, std::forward_iterator_tag>::value,
    bool>::type;
 
template <typename Container,
          typename InputIterator,
          IfIsNotForwardIterator<InputIterator> = true>
void reserveIfForwardIterator(Container *, InputIterator, InputIterator)
{
}
 
template <typename Container,
          typename ForwardIterator,
          IfIsForwardIterator<ForwardIterator> = true>
void reserveIfForwardIterator(Container *c, ForwardIterator f, ForwardIterator l)
{
    c->reserve(static_cast<typename Container::size_type>(std::distance(f, l)));
}
 
template <typename Iterator>
using KeyAndValueTest = decltype(
    std::declval<Iterator &>().key(),
    std::declval<Iterator &>().value()
);
 
template <typename Iterator>
using FirstAndSecondTest = decltype(
    (*std::declval<Iterator &>()).first,
    (*std::declval<Iterator &>()).second
);
 
template <typename Iterator>
using IfAssociativeIteratorHasKeyAndValue =
    std::enable_if_t<qxp::is_detected_v<KeyAndValueTest, Iterator>, bool>;
 
template <typename Iterator>
using IfAssociativeIteratorHasFirstAndSecond =
    std::enable_if_t<
        std::conjunction_v<
            std::negation<qxp::is_detected<KeyAndValueTest, Iterator>>,
            qxp::is_detected<FirstAndSecondTest, Iterator>
        >, bool>;
 
template <typename Iterator>
using MoveBackwardsTest = decltype(
    std::declval<Iterator &>().operator--()
);
 
template <typename Iterator>
using IfIteratorCanMoveBackwards =
    std::enable_if_t<qxp::is_detected_v<MoveBackwardsTest, Iterator>, bool>;
 
template <typename T, typename U>
using IfIsNotSame =
    typename std::enable_if<!std::is_same<T, U>::value, bool>::type;
 
template<typename T, typename U>
using IfIsNotConvertible = typename std::enable_if<!std::is_convertible<T, U>::value, bool>::type;
 
template <typename Container, typename Predicate>
auto sequential_erase_if(Container &c, Predicate &pred)
{
    // This is remove_if() modified to perform the find_if step on
    // const_iterators to avoid shared container detaches if nothing needs to
    // be removed. We cannot run remove_if after find_if: doing so would apply
    // the predicate to the first matching element twice!
 
    const auto cbegin = c.cbegin();
    const auto cend = c.cend();
    const auto t_it = std::find_if(cbegin, cend, pred);
    auto result = std::distance(cbegin, t_it);
    if (result == c.size())
        return result - result; // `0` of the right type
 
    // now detach:
    const auto e = c.end();
 
    auto it = std::next(c.begin(), result);
    auto dest = it;
 
    // Loop Invariants:
    // - it != e
    // - [next(it), e[ still to be checked
    // - [c.begin(), dest[ are result
    while (++it != e) {
        if (!pred(*it)) {
            *dest = std::move(*it);
            ++dest;
        }
    }
 
    result = std::distance(dest, e);
    c.erase(dest, e);
    return result;
}
 
template <typename Container, typename T>
auto sequential_erase(Container &c, const T &t)
{
    // use the equivalence relation from http://eel.is/c++draft/list.erasure#1
    auto cmp = [&](const auto &e) -> bool { return e == t; };
    return sequential_erase_if(c, cmp); // can't pass rvalues!
}
 
template <typename Container, typename T>
auto sequential_erase_with_copy(Container &c, const T &t)
{
    using CopyProxy = std::conditional_t<std::is_copy_constructible_v<T>, T, const T &>;
    return sequential_erase(c, CopyProxy(t));
}
 
template <typename Container, typename T>
auto sequential_erase_one(Container &c, const T &t)
{
    const auto cend = c.cend();
    const auto it = std::find(c.cbegin(), cend, t);
    if (it == cend)
        return false;
    c.erase(it);
    return true;
}
 
template <typename T, typename Predicate>
qsizetype qset_erase_if(QSet<T> &set, Predicate &pred)
{
    qsizetype result = 0;
    auto it = set.cbegin();
    auto e = set.cend(); // stable across detach (QHash::end() is a stateless sentinel)...
    while (it != e) {
        if (pred(*it)) {
            ++result;
            it = set.erase(it);
            e = set.cend(); // ...but re-set nonetheless, in case at some point it won't be
        } else {
            ++it;
        }
    }
    return result;
}
 
 
// Prerequisite: F is invocable on ArgTypes
template <typename R, typename F, typename ... ArgTypes>
struct is_invoke_result_explicitly_convertible : std::is_constructible<R, std::invoke_result_t<F, ArgTypes...>>
{};
 
// is_invocable_r checks for implicit conversions, but we need to check
// for explicit conversions in remove_if. So, roll our own trait.
template <typename R, typename F, typename ... ArgTypes>
constexpr bool is_invocable_explicit_r_v = std::conjunction_v<
    std::is_invocable<F, ArgTypes...>,
    is_invoke_result_explicitly_convertible<R, F, ArgTypes...>
>;
 
template <typename Container, typename Predicate>
auto associative_erase_if(Container &c, Predicate &pred)
{
    // we support predicates callable with either Container::iterator
    // or with std::pair<const Key &, Value &>
    using Iterator = typename Container::iterator;
    using Key = typename Container::key_type;
    using Value = typename Container::mapped_type;
    using KeyValuePair = std::pair<const Key &, Value &>;
 
    typename Container::size_type result = 0;
 
    auto it = c.begin();
    const auto e = c.end();
    while (it != e) {
        if constexpr (is_invocable_explicit_r_v<bool, Predicate &, Iterator &>) {
            if (pred(it)) {
                it = c.erase(it);
                ++result;
            } else {
                ++it;
            }
        } else if constexpr (is_invocable_explicit_r_v<bool, Predicate &, KeyValuePair &&>) {
            KeyValuePair p(it.key(), it.value());
            if (pred(std::move(p))) {
                it = c.erase(it);
                ++result;
            } else {
                ++it;
            }
        } else {
            static_assert(type_dependent_false<Container>(), "Predicate has an incompatible signature");
        }
    }
 
    return result;
}
 
} // namespace QtPrivate
 
QT_END_NAMESPACE
 
#endif // QCONTAINERTOOLS_IMPL_H