Re: [boost] shared_ptr_updates.zip

From: Greg Colvin (gcolvin_at_[hidden])
Date: 2001-07-25 15:34:50

As I replied on the earlier branch, I think this is a useful proposal, but
I still like having a separate finalizer function for shared_ptr.

> I suggested in a branch from the earlier thread that maybe the "finalizer"
> function, as you put it, would best be served by a separate class (or set of
> classes - one for shared one for basic scoped) that are tailored for true
> "initialisation is resource aquisition" needs.
> This could also contain non pointer types.
> My proposal is for:
> shared_resource<T> and
> scoped_resource<T>.
> 
> The constructors would take two arguments: an opaque handle of type T (not
> T*) and a finalizer function, which is a function, or functor, that takes
> one argument of type T and may or may not return (return value is ignored)
> (functions which take more arguments could be supported by functor binders).
> 
> It would also need a policy for how to handle uninitialised resources (in
> the case of the FILE example, and probably partialy specialised by default
> for all pointer types, it would, by default, test against NULL and could,
> for example, throw an exception).
> Throwing an exception for invalid FILEs returned from fopen would solve your
> problem with fclose crashing because the destructor would not be called.
> 
> I think this solution more neatly diverges true pointer-to-object semantics
> from initialisation-is-resource-aquisition semantics, rather than trying to
> overload the existing classes with too much orthagonal functionality.
> 
> What do you think?
> 
> I could come up with an example implementation to get the ball rolling (when
> I have some more time a bit later), but I think what I have said above
> captures most of it. I have not fully thought through the implications and
> side-effects yet, so any comments are welcome.
> 
> [)o
> IhIL..
> 
> > -----Original Message-----
> > From: Peter Dimov [mailto:pdimov_at_[hidden]]
> > Sent: 25 July 2001 21:55
> > To: boost_at_[hidden]
> > Subject: [boost] shared_ptr_updates.zip
> >
> >
> > shared_ptr_updates.zip in the smart_ptr folder contains an updated
> > shared_ptr that accepts a 'finalizer' function as a second argument.
> > Unfortunately
> >
> > shared_ptr<FILE> file_ptr(fopen(file_name,file_mode),fclose);
> >
> > is not a very good example of its functionality because fclose()
> > will crash
> > when called with a NULL argument. :-)
> >
> > This version is a bit more taxing so I don't know what the regression test
> > will say about it. The tests work on my compilers.
> >
> > --
> > Peter Dimov
> > Multi Media Ltd.
> >
> >
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> 
> 
> 
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