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Subject: Re: [boost] std::map::find() wrapper
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2011-05-04 14:24:26

Olaf van der Spek wrote:
> On Wed, May 4, 2011 at 3:08 PM, Stewart, Robert
> <Robert.Stewart_at_[hidden]> wrote:
> > Olaf van der Spek wrote:
> >> I'm not sure what your code looks like, but IMO bare
> >> pointers are perfectly fine in certain situations.
> >> Like this one, where no ownership issues are present.
> >
> > A function that returns a pointer immediately begs the
> > question of ownership. It is perfectly reasonable to think
> > that one should call delete on such a pointer when finished
> > with it. That, of course, would have nasty consequences, but
> > it is the result of returning a pointer.
> Is it? I've no idea why that would be reasonable. You don't
> delete something just because you can.

It is common for those without sufficient knowledge of smart pointers to return raw pointers from a functions that allocate the memory. Such programmers would suspect the calling code owns the memory referenced by the raw pointer. Thus, such an interface can be a source of errors.

That a person can so readily delete the return value with the attendant ill effects on the container make the interface problematic. An interface that returns a reference doesn't have the same problem. The caller must take the address and then delete it, which requires conscious misuse.

> > Local conventions may dictate that all ownership transfers
> > are done via std::auto_ptr, for example, and never through
> > raw pointers, leaving raw pointers as non-owning, possibly
> > null references. Boost, however, is used in various places
> > with different conventions.
> You can't expect every single lib to follow your local
> convention, can you?

No. That was my point. Boost cannot assume local conventions to give proper meaning to a function returning a raw pointer and so should avoid doing so.

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

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