Re: [boost] [pimpl] Mini Review

Subject: Re: [boost] [pimpl] Mini Review
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2011-05-26 16:24:37

Artyom Beilis wrote:
> From: Sergiu Dotenco <sergiu.dotenco_at_[hidden]>
> > Am 26.05.2011 18:28, schrieb Artyom Beilis:
> > >> From: Sergiu  Dotenco <sergiu.dotenco_at_[hidden]>
> > >>  Am 26.05.2011 11:22, schrieb Artyom Beilis:
> > >>
> > >> You can't use std::auto_ptr for pimpl implementation
> > >> in portable code.  Doing so is undefined behavior. To
> > >> quote ISO/IEC 14882:2003 (§17.4.3.6, p. 329):
> > >>
> > >> "In particular, the effects are undefined in the
> > >> following cases:
> > >> [...]
> > >> — if an incomplete type (3.9) is used as a template
> > >> argument when instantiating a template component,
> > >> unless specifically allowed for that component."
> > >>
> > >> which applies to most standard  library  types.
> > >
> > > When you actually implement  Foo::~Foo() {} in cpp file
> > > the type of the data object is complete so  the destructor
> > > is installed correctly.

Not relevant.  Foo is an incomplete type and it is used as a template argument for std::auto_ptr in the header.

> > That's not correct.  std::auto_ptr<data> is an
> > instantiation which uses an incomplete type as template
> > argument. Providing an non-inline destructor doesn't
> > magically make the data struct used in your example a
> > complete type.
>
> The quote you provide is too general about the library
> requirements.

No.  It's right on point.

> Particularly, looking into auto_ptr. (20.4.5.1 C++/2003
> standard)
>
> ~auto_ptr() throw();
> Requires: The expression delete get() is well formed.
> Effects: delete get().
>
> The expression delete get() is well formed when ~auto_ptr() is
> called in the destructor of Foo::~Foo() defined in cpp file.

That doesn't negate the point about the template argument.

> So it fills auto_ptr requirements.

Nope.

> No problems I can see also I'm not aware of any compiler that
> does not handle this correctly (so far Intel, GCC, MSVC,
> SunStudio, HP's ACC, DECXX)

That doesn't mean the code is conforming.  You can choose to rely on UB in your code, but Boost strives to do better.

_____
Rob Stewart                           robert.stewart_at_[hidden]
Software Engineer                     using std::disclaimer;
Dev Tools & Components
Susquehanna International Group, LLP  http://www.sig.com





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