Re: [boost] Suggestion for weak_ptr's

From: Rob Stewart (stewart_at_[hidden])
Date: 2004-08-18 11:35:12

From: "Peter Dimov" <pdimov_at_[hidden]>
> Jeff Williams wrote:
> >
> > struct foo { virtual ~foo() { } };
> > struct bar : foo { };
> >
> > typedef shared_ptr<foo> fooptr;
> > typedef shared_ptr<bar> barptr;
> >
> > void some_func(weak_ptr<foo> wf)
> > {
> >   barptr pb = wf.lock<bar>();
> > }
> >
> > // currently the way to do this is (as I am sure everyone knows)
> > void some_func(weak_ptr<foo> wf)
> > {
> >   barptr pb = dynamic_pointer_cast<bar>(wf.lock());
> > }
> >
> > My suggestion seems easier to read.  Would require no additional
> > overhead and would preserve existing behavior.
> 
> However, there is no indication that wf.lock<bar> does a cast, or which kind 
> of cast is being done.

Typically, hiding needed casts in a function is beneficial, and
documentation can take care of explaining what's occuring under
the covers.

> > I suppose you could provide a static and dynamic version:
> >
> > lock_static<bar> and lock_dynamic<bar>
> >
> > Any thoughts?  Or is the general concensus that ideas like this are
> > something indivudual people should do in their own source?
> 
> Something like that. In general, libraries expose a "minimal but complete" 
> interface, and utility functions are left to the users (whose preferences 
> usually differ).
> 
> "Boilerplate" functions or components (nearly every user needs to have them, 
> and they are a de-facto standard) are an exception, of course.

The better way to handle such extensions is via non-member
function templates:

   barptr pb = lock<bar>(wf);

Such function templates can be put in various places, as
appropriate, but they don't have to clutter weak_ptr's header
unless they are widely applicable.

That syntax has the advantage of being useful with other types,
too, if warranted.

-- 
Rob Stewart                           stewart_at_[hidden]
Software Engineer                     http://www.sig.com
Susquehanna International Group, LLP  using std::disclaimer;