318625 - Add nsTArray.AppendElement() that doesn't copy-construct

Status: RESOLVED FIXED

(Core :: XPCOM, enhancement)

Description

[Benjamin Smedberg]

When doing bug 316416 darin and I found that we wanted to avoid copy-construction when appending nsTArray elements. A new signature elem_type* AppendElement() will construct a new element in place.

Comment 1

[Benjamin Smedberg]

Attachment: AppendElement(), rev. 1

Comment 2

[Darin Fisher]

Comment on attachment 204734 [details] [diff] [review]
AppendElement(), rev. 1

>Index: xpcom/glue/nsTArray.h

>+    // Append a new element without constructing. This is useful to avoid
>+    // extra temporaries.
>+    elem_type* AppendElement() {
>+      if (!EnsureCapacity(Length() + 1, sizeof(elem_type)))
>+         return nsnull;
>+      elem_type* elem = new (Elements() + Length()) elem_type();
>+      ++mLength;
>+      return elem;
>+    }

I think this should use "elem_traits::Construct" so that we can
could specialize nsTArrayElementTraits<E> as needed.

Also, how about adding a similar version of InsertElementAt?

Please document the return value.

Comment 3

[Benjamin Smedberg]

Attachment: AppendElement(), rev. 2

Comment 4

[Darin Fisher]

Comment on attachment 204752 [details] [diff] [review]
AppendElement(), rev. 2

>Index: xpcom/glue/nsTArray.h

>+      nsTArrayElementTraits<E>::Construct(elem);

I wrote elem_traits::Construct for a reason! ;-)

Please change the code accordingly.

r=darin

Comment 5

[Benjamin Smedberg]

Bah, reading all those pretty typedefs is easier than writing them. Fixed on trunk.