Bug 450881: Add helpers for XPIDL arrays to nsCOMArray, r=froydnj

xpcom/glue/nsCOMArray.cpp

@@ -278,3 +278,29 @@ nsCOMArray_base::SizeOfExcludingThis(
 
     return n;
 }
+
+
+void
+nsCOMArray_base::Adopt(nsISupports** aElements, uint32_t aSize)
+{
+    Clear();
+    mArray.AppendElements(aElements, aSize);
+
+    // Free the allocated array as well.
+    NS_Free(aElements);
+}
+
+uint32_t
+nsCOMArray_base::Forget(nsISupports*** elements)
+{
+    uint32_t length = Length();
+    size_t array_size = sizeof(nsISupports*) * length;
+    nsISupports** array = static_cast<nsISupports**>(NS_Alloc(array_size));
+    memmove(array, Elements(), array_size);
+    *elements = array;
+    // Don't Release the contained pointers; the caller of the method will
+    // do this eventually.
+    mArray.Clear();
+
+    return length;
+}

xpcom/glue/nsCOMArray.h

@@ -89,6 +89,8 @@ protected:
         mArray.SwapElements(aOther.mArray);
     }
 
+    void Adopt(nsISupports** aElements, uint32_t aCount);
+    uint32_t Forget(nsISupports*** aElements);
 public:
     // elements in the array (including null elements!)
     int32_t Count() const {
@@ -230,8 +232,16 @@ class nsCOMArray : public nsCOMArray_base
     explicit
     nsCOMArray(const nsCOMArray<T>& aOther) : nsCOMArray_base(aOther) { }
 
+    nsCOMArray(nsCOMArray<T>&& aOther) { SwapElements(aOther); }
+
     ~nsCOMArray() {}
 
+    // We have a move assignment operator, but no copy assignment operator.
+    nsCOMArray<T>& operator=(nsCOMArray<T>&& aOther) {
+        SwapElements(aOther);
+        return *this;
+    }
+
     // these do NOT refcount on the way out, for speed
     T* ObjectAt(int32_t aIndex) const {
         return static_cast<T*>(nsCOMArray_base::ObjectAt(aIndex));
@@ -387,6 +397,35 @@ class nsCOMArray : public nsCOMArray_base
                  aMallocSizeOf, aData);
     }
 
+    /**
+     * Adopt parameters that resulted from an XPIDL outparam. The aElements
+     * parameter will be freed as a result of the call.
+     *
+     * Example usage:
+     * nsCOMArray<nsISomeInterface> array;
+     * nsISomeInterface** elements;
+     * uint32_t length;
+     * ptr->GetSomeArray(&elements, &length);
+     * array.Adopt(elements, length);
+     */
+    void Adopt(T** aElements, uint32_t aSize) {
+        nsCOMArray_base::Adopt(reinterpret_cast<nsISupports**>(aElements),
+            aSize);
+    }
+
+    /**
+     * Export the contents of this array to an XPIDL outparam. The array will be
+     * Clear()'d after this operation.
+     *
+     * Example usage:
+     * nsCOMArray<nsISomeInterface> array;
+     * *length = array.Forget(retval);
+     */
+    uint32_t Forget(T*** elements) {
+        return nsCOMArray_base::Forget(
+            reinterpret_cast<nsISupports***>(elements));
+    }
+
 private:
 
     // don't implement these!