Re: Initialization and Finalization of limited object "returned" by a function

[Adam Beneschan <adam@irvine.com>]

On Feb 11, 11:10 am, Robert A Duff <bobd...@shell01.TheWorld.com>
wrote:
> Adam Beneschan <a...@irvine.com> writes:
> > But more simply, as I understand it: (1) When you have an extended
> > return, the return object is used as the anonymous object that holds
> > the function result at the point of the function call, so it's not
> > finalized until the caller is done with the anonymous object; and (2)
> > when the object is built in place, the anonymous object "mutates into"
> > the new object and is not finalized (7.6(17.7/3)).  So yes, no
> > finalization should be done until X goes out of scope.
>
> Just to be clear: There's nothing particularly special about
> extended return statements, other than the fact that they
> provide a name for the result.  

That last is an important distinction, however.  A function call
involves (conceptually) an anonymous object.  For a normal return (for
a non-limited type):

   return Some_Expression;

Some_Expression is computed and then assigned into the anonymous
object.  This assignment involves an Adjust.  Then, at some point,
whatever objects went into creating Some_Expression will get finalized
when the function exits.  If Some_Expression is a local variable, for
instance, that variable will get finalized.  If some other temporary
needs to be created in order to hold the value of Some_Expression,
that temporary will be finalized.

For an extended return,

   return R : T;

R is not a local variable, and it isn't "assigned" into the anonymous
object; thus, there's no Adjust, and R is not finalized when the
function returns (but the anonymous object will be finalized later,
except when it mutates into some other object).  I think that's the
point of the nasty language in 3.10.2(10.1).  Which is another way of
saying that R is a name for the result (as you said), not a distinct
object that gets copied to the result.  I thought it would be helpful
to point it out---not to you, but to other readers.  It's hardly a
trivial difference, and it's an important one to understand when
adjusts and finalizations are involved.  Anyway, I hope this helps
someone.

                                   -- Adam