qt-everywhere-src-5.15.1/qtbase/src/corelib/tools/qoffsetstringarray_p.h

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#ifndef QOFFSETSTRINGARRAY_P_H
#define QOFFSETSTRINGARRAY_P_H

//
//  W A R N I N G
//  -------------
//
// This file is not part of the Qt API.  It exists purely as an
// implementation detail.  This header file may change from version to
// version without notice, or even be removed.
//
// We mean it.
//

#include "private/qglobal_p.h"

#include <tuple>
#include <array>

QT_BEGIN_NAMESPACE

namespace QtPrivate {
template<int N, int O, int I, int ... Idx>
struct OffsetSequenceHelper : OffsetSequenceHelper<N - 1, O + I, Idx..., O> { };

template<int Last, int I, int S, int ... Idx>
struct OffsetSequenceHelper<1, Last, I, S, Idx...> : IndexesList<Last + I, Idx..., Last>
{
    static const constexpr auto Length = Last + I;
    using Type = typename std::conditional<
        Last <= std::numeric_limits<quint8>::max(),
        quint8,
        typename std::conditional<
            Last <= std::numeric_limits<quint16>::max(),
            quint16,
            int>::type
        >::type;
};

template<int ... Idx>
struct OffsetSequence : OffsetSequenceHelper<sizeof ... (Idx), 0, Idx..., 0> { };

template<int N>
struct StaticString
{
    const char data[N];
};


template<>
struct StaticString<0>
{
    static constexpr int size() noexcept
    {
        return 0;
    }
};

template<typename, typename>
struct StaticStringBuilder;

template<int ... I1, int ... I2>
struct StaticStringBuilder<IndexesList<I1...>, IndexesList<I2...>>
{

QT_WARNING_PUSH
QT_WARNING_DISABLE_MSVC(4100) // The formal parameter is not referenced in the body of the function.
                              // The unreferenced parameter is ignored.
                              // It happens when 'rs' is StaticString<0>
    template<int N1, int N2>
    static constexpr StaticString<N1 + N2> concatenate(
        const char (&ls)[N1], const StaticString<N2> &rs) noexcept
    {
        return StaticString<N1 + N2>{{ls[I1]..., rs.data[I2]...}};
    }
QT_WARNING_POP
};

template<int Sum>
constexpr StaticString<0> staticString() noexcept
{
    return StaticString<0>{};
}

QT_WARNING_PUSH
QT_WARNING_DISABLE_MSVC(4503)
template<int Sum, int I, int ... Ix>
constexpr StaticString<Sum> staticString(const char (&s)[I], const char (&...sx)[Ix]) noexcept
{
    return StaticStringBuilder<
        makeIndexSequence<I>,
        makeIndexSequence<Sum - I>>::concatenate(s, staticString<Sum - I>(sx...));
}
QT_WARNING_POP
} // namespace QtPrivate

template<typename T, int SizeString, int SizeOffsets>
class QOffsetStringArray
{
public:
    using Type = T;

    template<int ... Ox>
    constexpr QOffsetStringArray(const QtPrivate::StaticString<SizeString> &str,
                                 QtPrivate::IndexesList<SizeString, Ox...>) noexcept
        : m_string(str),
          m_offsets{Ox...}
    { }

    constexpr inline const char *operator[](const int index) const noexcept
    {
        return m_string.data + m_offsets[qBound(int(0), index, SizeOffsets - 1)];
    }

    constexpr inline const char *at(const int index) const noexcept
    {
        return m_string.data + m_offsets[index];
    }

    constexpr inline const char *str() const { return m_string.data; }
    constexpr inline const T *offsets() const { return m_offsets; }
    constexpr inline int count() const { return SizeOffsets; };

    static constexpr const auto sizeString = SizeString;
    static constexpr const auto sizeOffsets = SizeOffsets;

private:
    QtPrivate::StaticString<SizeString> m_string;
    const T m_offsets[SizeOffsets];
};

template<typename T, int N, int ... Ox>
constexpr QOffsetStringArray<T, N, sizeof ... (Ox)> qOffsetStringArray(
    const QtPrivate::StaticString<N> &string,
    QtPrivate::IndexesList<N, Ox...> offsets) noexcept
{
    return QOffsetStringArray<T, N, sizeof ... (Ox)>(
               string,
               offsets);
}

template<int ... Nx>
struct QOffsetStringArrayRet
{
    using Offsets = QtPrivate::OffsetSequence<Nx...>;
    using Type = QOffsetStringArray<typename Offsets::Type, Offsets::Length, sizeof ... (Nx)>;
};

template<int ... Nx>
constexpr auto qOffsetStringArray(const char (&...strings)[Nx]) noexcept -> typename QOffsetStringArrayRet<Nx...>::Type
{
    using Offsets = QtPrivate::OffsetSequence<Nx...>;
    return qOffsetStringArray<typename Offsets::Type>(
            QtPrivate::staticString<Offsets::Length>(strings...), Offsets{});
}

QT_END_NAMESPACE

#endif // QOFFSETSTRINGARRAY_P_H