From: Rob Stewart (stewart_at_[hidden])
Date: 2005-04-28 14:03:43
From: Jason Hise <chaos_at_[hidden]>
> Rob Stewart wrote:
>
> >As I understand it, the operation is inherently unsafe; it isn't
> >a matter of efficiency, or even desirable usage. Given that, it
> >is most appropriate that you spell things differently. You want
> >to call attention to such usage.
> >
> Even though the usage is undesirable, it may still be necessary in cases
> where the singleton needs to behave polymorphically like one of its base
> classes.
But you said that the object may not exist since it is
operator ->() that does the lifetime management. Thus, the
object may not actually exist when you call the unsafe function,
so it is a dangerous operation. Did I misunderstand something?
> >Having said that, is it really the case that operator *()
> >couldn't do the same work as operator ->() (possibly adding an
> >exception if you can't get the underlying object)?
> >
> The difference is that the pointer returned by operator -> is guaranteed
> to be used immediately, and by using an intermediate pointer class I can
> construct a lock for the duration of the member call (this technique is
> described in Modern C++ Design, in the smart pointer section).
So you're returning a proxy from operator ->(), right?
> Operator * is incapable of constructing this type of temporary lock, and
> additionally there is no guarantee that the reference returned would
> used and discarded immediately. Once the actual reference is returned,
> no more checking can take place.
Why can't you return such a proxy from a member function like
"get" or "get_object" and let that proxy convert to the singleton
type?
That means you can spell "get_unsafe_ptr" without "unsafe"
because the proxy ensures that it is safe (as safe as with
operator ->(), anyway).
-- Rob Stewart stewart_at_[hidden] Software Engineer http://www.sig.com Susquehanna International Group, LLP using std::disclaimer;