Re: Design question related to std::auto_ptr

From:

abhay.burli@gmail.com

Newsgroups:

comp.lang.c++

Date:

Mon, 23 Mar 2009 02:22:08 -0700 (PDT)

Message-ID:

<bc2043c2-16b8-4ebd-80e5-433bd781772d@p6g2000pre.googlegroups.com>

On Mar 23, 2:13 pm, "Alf P. Steinbach" <al...@start.no> wrote:

Well, the PIMPL idiom is a/the prime example of taking advantage of this
property -- or lack of requirement -- of boost::shared_ptr.

[snip]
I.e., in the implementation file it goes like this:

class Foo::Impl {}; // Complete definition of Impl =

class.

Foo::Foo()
: myPImpl( new Impl ) // shared_ptr has all info it nee=

ds here.

{}

Thanks, this is exactly what i was thinking of.

Some folks have argued that the same technique must in practice have to w=

ork

nicely also for std::auto_ptr, at least if also Foo::~Foo() is defined in=

the

implementation file, because how could any compiler manage to screw up th=

ings

then? But according to the standard's general rules it's just UB to do it=

with

std::auto_ptr. And one risks the compiler warning about that UB, as above=

..

Can you kindly explain why this is the case? I thought the original
example produces a warning because the compiler tries to generate an
implicit dtor which may be orthogonal for polymorphic types like
virtual ~Dtor() {}.

Regards,
Abhay