Q(Any|Utf8)StringView: move array size deduction feature to fromArray

The constructor taking an array literal will now stop at the first
null-terminator encountered.

And fromArray is introduced which only supports array literals.
Constructs a view of the full size. Explicit so it shouldn't be
surprising.

Change-Id: I1497c33a5c12453a95e87c990abe6335b2817081
Reviewed-by: Andrei Golubev <andrei.golubev@qt.io>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

src/corelib/doc/snippets/code/src_corelib_text_qanystringview.cpp

@@ -54,6 +54,6 @@
 //! [0]
 
 //! [2]
-    auto sv1 = QAnyStringView{std::begin(array), std::end(array)}; // using C++11 std::begin()/std::end()
-    auto sv2 = QAnyStringView(array, std::size(array)); // using C++17 std::size()
+    auto sv1 = QAnyStringView{std::begin(array), std::end(array) - 1}; // using C++11 std::begin()/std::end()
+    auto sv2 = QAnyStringView(array, std::size(array) - 1); // using C++17 std::size()
 //! [2]

src/corelib/doc/snippets/code/src_corelib_text_qstringview.cpp

@@ -56,7 +56,3 @@
 //! [1]
     void fun(QChar ch) { fun(QStringView(&ch, 1)); }
 //! [1]
-
-//! [2]
-    auto sv = QStringView(array, std::size(array)); // using C++17 std::size()
-//! [2]

src/corelib/doc/snippets/code/src_corelib_text_qutf8stringview.cpp

@@ -52,8 +52,3 @@
     void myfun1(QUtf8StringView sv);        // preferred
     void myfun2(const QUtf8StringView &sv); // compiles and works, but slower
 //! [0]
-
-//! [2]
-    auto sv1 = QUtf8StringView{std::begin(array), std::end(array)}; // using C++11 std::begin()/std::end()
-    auto sv2 = QUtf8StringView(array, std::size(array)); // using C++17 std::size()
-//! [2]

src/corelib/text/qanystringview.h

@@ -109,9 +109,11 @@ private:
     }
 
     template <typename Char, size_t N>
-    static constexpr qsizetype lengthHelperContainer(const Char (&)[N]) noexcept
+    static constexpr qsizetype lengthHelperContainer(const Char (&str)[N]) noexcept
     {
-        return qsizetype(N - 1);
+        const auto it = std::char_traits<Char>::find(str, N, Char(0));
+        const auto end = it ? it : std::next(str, N);
+        return qsizetype(std::distance(str, end));
     }
 
     static QChar toQChar(char ch) noexcept { return toQChar(QLatin1Char{ch}); } // we don't handle UTF-8 multibytes
@@ -180,6 +182,10 @@ public:
     constexpr QAnyStringView(QBasicUtf8StringView<UseChar8T> v) noexcept
         : QAnyStringView(std::data(v), lengthHelperContainer(v)) {}
 
+    template <typename Char, size_t Size, if_compatible_char<Char> = true>
+    [[nodiscard]] constexpr static QAnyStringView fromArray(const Char (&string)[Size]) noexcept
+    { return QAnyStringView(string, Size); }
+
     // defined in qstring.h:
     template <typename Visitor>
     inline constexpr decltype(auto) visit(Visitor &&v) const;

src/corelib/text/qanystringview.qdoc

@@ -197,11 +197,9 @@
     \fn template <typename Char, size_t N> QAnyStringView::QAnyStringView(const Char (&string)[N])
 
     Constructs a string view on the character string literal \a string.
-    The length is set to \c{N-1}, excluding the trailing \c{Char(0)}.
-    If you need the full array, use the constructor from pointer and
-    size instead:
-
-    \snippet code/src_corelib_text_qanystringview.cpp 2
+    The view covers the array until the first \c{Char(0)} is encountered,
+    or \c N, whichever comes first.
+    If you need the full array, use fromArray() instead.
 
     \a string must remain valid for the lifetime of this string view
     object.
@@ -250,6 +248,27 @@
     \sa isNull(), isEmpty(), {Compatible Character Types}
 */
 
+/*!
+    \fn template <typename Char, size_t Size> static QAnyStringView fromArray(const Char (&string)[Size]) noexcept
+
+    Constructs a string view on the full character string literal \a string,
+    including any trailing \c{Char(0)}. If you don't want the
+    null-terminator included in the view then you can use the constructor
+    overload taking a pointer and a size:
+
+    \snippet code/src_corelib_text_qanystringview.cpp 2
+
+    Alternatively you can use the constructor overload taking an
+    array literal which will create a view up to, but not including,
+    the first null-terminator in the data.
+
+    \a string must remain valid for the lifetime of this string view
+    object.
+
+    This function will work with any array literal if \c Char is a
+    compatible character type.
+*/
+
 /*!
     \fn QString QAnyStringView::toString() const
 

src/corelib/text/qstringview.cpp

@@ -278,11 +278,9 @@ QT_BEGIN_NAMESPACE
     \fn template <typename Char, size_t N> QStringView::QStringView(const Char (&string)[N])
 
     Constructs a string view on the character string literal \a string.
-    The length is set to \c{N-1}, excluding the trailing \{Char(0)}.
-    If you need the full array, use the constructor from pointer and
-    size instead:
-
-    \snippet code/src_corelib_text_qstringview.cpp 2
+    The view covers the array until the first \c{Char(0)} is encountered,
+    or \c N, whichever comes first.
+    If you need the full array, use fromArray() instead.
 
     \a string must remain valid for the lifetime of this string view
     object.
@@ -292,6 +290,8 @@ QT_BEGIN_NAMESPACE
     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.
+
+    \sa fromArray
 */
 
 /*!
@@ -323,6 +323,25 @@ QT_BEGIN_NAMESPACE
     \sa isNull(), isEmpty()
 */
 
+/*!
+    \fn template <typename Char, size_t Size> static QStringView fromArray(const Char (&string)[Size]) noexcept
+
+    Constructs a string view on the full character string literal \a string,
+    including any trailing \c{Char(0)}. If you don't want the
+    null-terminator included in the view then you can chop() it off
+    when you are certain it is at the end. Alternatively you can use
+    the constructor overload taking an array literal which will create
+    a view up to, but not including, the first null-terminator in the data.
+
+    \a string must remain valid for the lifetime of this string view
+    object.
+
+    This function will work with any array literal 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 QString QStringView::toString() const
 

src/corelib/text/qstringview.h

@@ -172,9 +172,11 @@ private:
     }
 
     template <typename Char, size_t N>
-    static constexpr qsizetype lengthHelperContainer(const Char (&)[N]) noexcept
+    static constexpr qsizetype lengthHelperContainer(const Char (&str)[N]) noexcept
     {
-        return qsizetype(N - 1);
+        const auto it = std::char_traits<Char>::find(str, N, Char(0));
+        const auto end = it ? it : std::next(str, N);
+        return qsizetype(std::distance(str, end));
     }
 
     template <typename Char>
@@ -223,6 +225,10 @@ public:
     constexpr QStringView(const Container &c) noexcept
         : QStringView(std::data(c), lengthHelperContainer(c)) {}
 
+    template <typename Char, size_t Size, if_compatible_char<Char> = true>
+    [[nodiscard]] constexpr static QStringView fromArray(const Char (&string)[Size]) noexcept
+    { return QStringView(string, Size); }
+
     Q_REQUIRED_RESULT inline QString toString() const; // defined in qstring.h
 #if defined(Q_OS_DARWIN) || defined(Q_QDOC)
     // defined in qcore_foundation.mm

src/corelib/text/qutf8stringview.h

@@ -160,9 +160,11 @@ private:
     // Note: Do not replace with std::size(const Char (&)[N]), cause the result
     // will be of by one.
     template <typename Char, size_t N>
-    static constexpr qsizetype lengthHelperContainer(const Char (&)[N]) noexcept
+    static constexpr qsizetype lengthHelperContainer(const Char (&str)[N]) noexcept
     {
-        return qsizetype(N - 1);
+        const auto it = std::char_traits<Char>::find(str, N, Char(0));
+        const auto end = it ? it : std::next(str, N);
+        return qsizetype(std::distance(str, end));
     }
 
     template <typename Char>
@@ -216,6 +218,10 @@ public:
         : QBasicUtf8StringView(other.data(), other.size()) {}
 #endif
 
+    template <typename Char, size_t Size, if_compatible_char<Char> = true>
+    [[nodiscard]] constexpr static QBasicUtf8StringView fromArray(const Char (&string)[Size]) noexcept
+    { return QBasicUtf8StringView(string, Size); }
+
     [[nodiscard]] inline QString toString() const; // defined in qstring.h
 
     [[nodiscard]] constexpr qsizetype size() const noexcept { return m_size; }

src/corelib/text/qutf8stringview.qdoc

@@ -318,11 +318,9 @@
     \fn template <typename Char, size_t N> QUtf8StringView::QUtf8StringView(const Char (&string)[N])
 
     Constructs a string view on the character string literal \a string.
-    The length is set to \c{N-1}, excluding the trailing \c{Char(0)}.
-    If you need the full array, use the constructor from pointer and
-    size instead:
-
-    \snippet code/src_corelib_text_qutf8stringview.cpp 2
+    The view covers the array until the first \c{Char(0)} is encountered,
+    or \c N, whichever comes first.
+    If you need the full array, use fromArray() instead.
 
     \a string must remain valid for the lifetime of this string view
     object.
@@ -331,6 +329,8 @@
     is an actual array and if \c Char is a compatible character type. The
     compatible character types are: \c char8_t, \c char, \c{signed char} and
     \c{unsigned char}.
+
+    \sa fromArray
 */
 
 /*!
@@ -352,6 +352,24 @@
     \sa isNull(), isEmpty()
 */
 
+/*!
+    \fn template <typename Char, size_t Size> static QBasicUtf8StringView fromArray(const Char (&string)[Size])
+
+    Constructs a string view on the full character string literal \a string,
+    including any trailing \c{Char(0)}. If you don't want the
+    null-terminator included in the view then you can chop() it off
+    when you are certain it is at the end. Alternatively you can use
+    the constructor overload taking an array literal which will create
+    a view up to, but not including, the first null-terminator in the data.
+
+    \a string must remain valid for the lifetime of this string view
+    object.
+
+    This function will work with any array literal if \c Char is a
+    compatible character type. The compatible character types
+    are: \c char8_t, \c char, \c{signed char} and \c{unsigned char}.
+*/
+
 /*!
     \fn QString QUtf8StringView::toString() const
 

tests/auto/corelib/text/qstringview/tst_qstringview.cpp

@@ -157,6 +157,7 @@ private Q_SLOTS:
     void constExpr() const;
     void basics() const;
     void literals() const;
+    void fromArray() const;
     void at() const;
 
     void arg() const;
@@ -425,10 +426,41 @@ void tst_QStringView::literals() const
     }
 
     // these are different results
-    QCOMPARE(size_t(QStringView(withnull).size()), sizeof(withnull)/sizeof(withnull[0]) - 1);
+    QCOMPARE(size_t(QStringView(withnull).size()), 1);
+    QCOMPARE(size_t(QStringView::fromArray(withnull).size()), sizeof(withnull)/sizeof(withnull[0]));
     QCOMPARE(QStringView(withnull + 0).size(), 1);
 }
 
+void tst_QStringView::fromArray() const
+{
+    static constexpr char16_t hello[] = u"Hello\0abc\0\0.";
+
+    constexpr QStringView sv = QStringView::fromArray(hello);
+    QCOMPARE(sv.size(), 13);
+    QVERIFY(!sv.empty());
+    QVERIFY(!sv.isEmpty());
+    QVERIFY(!sv.isNull());
+    QCOMPARE(*sv.data(), 'H');
+    QCOMPARE(sv[0],      'H');
+    QCOMPARE(sv.at(0),   'H');
+    QCOMPARE(sv.front(), 'H');
+    QCOMPARE(sv.first(), 'H');
+    QCOMPARE(sv[4],      'o');
+    QCOMPARE(sv.at(4),   'o');
+    QCOMPARE(sv[5],      '\0');
+    QCOMPARE(sv.at(5),   '\0');
+    QCOMPARE(*(sv.data() + sv.size() - 2),  '.');
+    QCOMPARE(sv.back(),  '\0');
+    QCOMPARE(sv.last(),  '\0');
+
+    const char16_t bytes[] = {u'a', u'b', u'c'};
+    QStringView sv2 = QStringView::fromArray(bytes);
+    QCOMPARE(sv2.data(), reinterpret_cast<const QChar *>(bytes + 0));
+    QCOMPARE(sv2.size(), 3);
+    QCOMPARE(sv2.first(), u'a');
+    QCOMPARE(sv2.last(), u'c');
+}
+
 void tst_QStringView::at() const
 {
     QString hello("Hello");