Re: auto_ptr in exception safety design

From:

David Wilkinson <no-reply@effisols.com>

Newsgroups:

microsoft.public.vc.language

Date:

Sat, 29 Mar 2008 07:52:39 -0400

Message-ID:

<ebRxkNZkIHA.4684@TK2MSFTNGP06.phx.gbl>

George wrote:

Hello everyone,

What I am confused is about,

http://www.gotw.ca/gotw/059.htm

--------------------
Indeed, often the best way to implement the Pimpl idiom is exactly as shown
in Example 4 above, by using a pointer (in order to take advantage of
nonthrowing operations) while still wrapping the dynamic resource safely in
an auto_ptr manager object. Just remember that now your object must provide
its own copy construction and assignment with the right semantics for the
auto_ptr member, or disable them if copy construction and assignment don't
make sense for the class.
--------------------

1. What means "the right semantics for the auto_ptr member"?

2. "disable" means for the class, copy construction and assignment are not
needed? Curious. Never thought of a class which does not need that two basic
functions. :-)

George:

1. I think it would be less confusing if it simply said

"Just remember that now your object must provide its own copy construction and
assignment as illustrated above, or disable them if copy construction and
assignment don't make sense for the class."

2. Lots of classes disable their copy constructor and assignment operator (by
making them private and not implementing them). One example is the MFC CWnd
class which wraps an HWND window handle. If CWnd were copyable, there would no
longer be a 1-1 correspondence between CWnd's and HWND's, which is required for
MFC to function correctly.

--
David Wilkinson
Visual C++ MVP