Re: Deriving from vector

From:

"Doug Harrison [MVP]" <dsh@mvps.org>

Newsgroups:

microsoft.public.vc.stl

Date:

Sat, 04 Aug 2007 19:14:33 -0500

Message-ID:

<665ab3d0qnff10k1fqd7j27snsnitkimue@4ax.com>

On Sat, 4 Aug 2007 16:06:00 -0700, Mick <Mick@discussions.microsoft.com>
wrote:

Interesting. We did this before in Visual Studio 6.0 and it worked okay. It
may not have been safe, but it did work. Our derived class' erase called the
base class to do the actual erasing.

It'll work, as long as you never do something like this:

void f(MyVector<int>& v1)
{
vector<int>& v2 = v1;
v2.erase(); // Calls vector::erase, not MyVector::erase
}

In addition, no vector member function should call the non-virtual erase
function you tried unsuccessfully to override. That could be the bigger
stumbling block, because who wants to exhaustively examine vector's
implementation?

It would then determine how much unused
memory was held by the collection and deallocate the excess once it reached a
certain amount.

How did it do that? (Except for the swap idiom, there's no documented way
to do it.)

Is there a way to have std::vector do something similar, without having to
do it manually outside of the class every time erase is called?

Like I said:

you can either derive privately from it or write a
new class that has a vector member. Then you control all access to the
vector and can expose only those operations and types that are needed.

--
Doug Harrison
Visual C++ MVP