QRingBuffer: simplify QRingChunk special member functions [2/2]

Use NSDMI and let the compiler generate the default ctor, too.

Statically assert that it's still noexcept (we marked it as such,
because MSVC still doesn't noexcept(auto) when an SMF is =default'ed.

Simplify the other ctors, too, relying on NSDMI. Keep one instance of
tailOffset(0), in the 'reserving' ctor, because it's inconsistent with
the other ctors which all do tailOffset{chunk.size()}, so it's best to
leave this explicit, lest the next reader wonders whether it was
forgotten.

Pick-to: 6.3
Change-Id: I0d9f91aa5bc89377c4144589df8786b502e956a4
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

2 files changed, 7 insertions, 9 deletions

diff --git a/src/corelib/tools/qringbuffer.cpp b/src/corelib/tools/qringbuffer.cpp
index b10362b0cd..72c56a20f6 100644
--- a/src/corelib/tools/qringbuffer.cpp
+++ b/src/corelib/tools/qringbuffer.cpp
@@ -47,6 +47,7 @@
 
 QT_BEGIN_NAMESPACE
 
+static_assert(std::is_nothrow_default_constructible_v<QRingChunk>);
 static_assert(std::is_nothrow_move_constructible_v<QRingChunk>);
 static_assert(std::is_nothrow_move_assignable_v<QRingChunk>);
 
diff --git a/src/corelib/tools/qringbuffer_p.h b/src/corelib/tools/qringbuffer_p.h
index 84e0f9ddec..58430b5a68 100644
--- a/src/corelib/tools/qringbuffer_p.h
+++ b/src/corelib/tools/qringbuffer_p.h
@@ -65,20 +65,17 @@ class QRingChunk
 {
 public:
     // initialization and cleanup
-    inline QRingChunk() noexcept :
-        headOffset(0), tailOffset(0)
-    {
-    }
+    QRingChunk() noexcept = default;
     explicit inline QRingChunk(qsizetype alloc) :
-        chunk(alloc, Qt::Uninitialized), headOffset(0), tailOffset(0)
+        chunk(alloc, Qt::Uninitialized), tailOffset(0)
     {
     }
     explicit inline QRingChunk(const QByteArray &qba) noexcept :
-        chunk(qba), headOffset(0), tailOffset(qba.size())
+        chunk(qba), tailOffset(qba.size())
     {
     }
     explicit QRingChunk(QByteArray &&qba) noexcept :
-        chunk(std::move(qba)), headOffset(0), tailOffset(chunk.size())
+        chunk(std::move(qba)), tailOffset(chunk.size())
     {
     }
 
@@ -164,8 +161,8 @@ public:
 
 private:
     QByteArray chunk;
-    qsizetype headOffset;
-    qsizetype tailOffset;
+    qsizetype headOffset = 0;
+    qsizetype tailOffset = 0;
 };
 Q_DECLARE_SHARED(QRingChunk)