TITLE: return value optimization and temp lifetimes

(Newsgroups: comp.lang.c++.moderated, 7 Mar 97)

BERGER:  "Micha S. Berger" <aishdas@IDT.NET>

|>  > We all know you can't do
|>  > int& foo() {
|>  >     int a = 3;
|>  >     return a;
|>  > }
|>  > 
|>  > So, on a job interview I was asked about how to return a reference,
|>  > without invoking new -- since new might lead to a memory link on the
|>  > part of an unaware user of your class/library.
|>  > 
|>  > (The case, I forget the details, involved nesting <<, so that you wanted
|>  > the left side to actually refer to the same object.)
|>  > 
|>  > Either way, after giving up (mumbling something about g++'s workaround),
|>  > the interview claims that according to CD2,
|>  >     return Foo(x);
|>  > will construct a Foo on the CALLER'S stack, not on the current
|>  > function's.
|>  > 
|>  > Sounded unlikely to me. Anyone see this written anywhere?


BLACK: "Paul Black" <paul.black@vf.vodafone.co.uk>

|>  Section 12.2 of CD2 is probably what you are looking for. Temporaries
|>  bound to a reference have the same lifetime as the reference.


KANZE: James Kanze <james-albert.kanze@vx.cit.alcatel.fr>

Not quite.  According to 12.2, a temporary bound to a reference persists
for the lifetime of the reference *OR* until the end of the scope in
which the temporary is created, whichever comes first.

In the above case, the scope in which the temporary is created is the
function; the temporary must be destructed on leaving the function.