Introduce QArrayDataOps::truncate

This enables a truncating resize() to be implemented. It is similar to
destroyAll(), but updates the size() as it goes, so it is safe to use
outside a container's destructor (and doesn't necessarily destroy all
elements).

The appendInitialize test was repurposed and now doubles as an
additional test for QArrayDataOps as well as exercising SimpleVector's
resize().

Change-Id: Iee94a685c9ea436c6af5b1b77486734a38c49ca1
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/src/corelib/tools/qarraydataops.h b/src/corelib/tools/qarraydataops.h
index 785a26c3a8..de149b701c 100644
--- a/src/corelib/tools/qarraydataops.h
+++ b/src/corelib/tools/qarraydataops.h
@@ -89,6 +89,14 @@ struct QPodArrayOps
         this->size += n;
     }
 
+    void truncate(size_t newSize)
+    {
+        Q_ASSERT(!this->ref.isShared());
+        Q_ASSERT(newSize < size_t(this->size));
+
+        this->size = newSize;
+    }
+
     void destroyAll() // Call from destructors, ONLY!
     {
         Q_ASSERT(this->ref.atomic.load() == 0);
@@ -153,6 +161,17 @@ struct QGenericArrayOps
         }
     }
 
+    void truncate(size_t newSize)
+    {
+        Q_ASSERT(!this->ref.isShared());
+        Q_ASSERT(newSize < size_t(this->size));
+
+        const T *const b = this->begin();
+        do {
+            (b + --this->size)->~T();
+        } while (uint(this->size) != newSize);
+    }
+
     void destroyAll() // Call from destructors, ONLY
     {
         // As this is to be called only from destructor, it doesn't need to be
@@ -239,6 +258,7 @@ struct QMovableArrayOps
 {
     // using QGenericArrayOps<T>::appendInitialize;
     // using QGenericArrayOps<T>::copyAppend;
+    // using QGenericArrayOps<T>::truncate;
     // using QGenericArrayOps<T>::destroyAll;
 
     void insert(T *where, const T *b, const T *e)