[Bug c++/26471] no warning available when binding a temporary to a const reference member

["o dot kullmann at swansea dot ac dot uk" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #4 from o dot kullmann at swansea dot ac dot uk  2006-02-25 21:21 -------
>   Y y((X()));
> 
> How does GCC know that the temporary that holds X() is going to be stored in y?

By the definition of Y, obviously. There seems to be a very special way of
how GCC is parsing the input, and from that it seems to follow that this
user error is hard to detect here. I simply argue from the user's point
of view, not from the gcc-system point of view.

> 
> > And finally, sure, books speak about lifetime of temporaries, but references
> > are badly covered. And then this special behaviour of binding to temporaries,
> > different for class members and block members, I carefully searched for it in
> > the 30 something C++ books I have, but didn't find anything. 
> 
> There is no special behavior really.  Maybe that is your misunderstanding.
> 

This behaviour is a special section in the standard: 12.2, paragraph 5 in
the standard: The first sentence states the "expected behaviour":

The temporary to which the reference is
bound or the temporary that is the complete object to a subobject of which the
temporary is bound persists
for the lifetime of the reference except as specified below.

(This is as one would expect from const references to a temporary at block
scope --- it's the lifetime of the reference which "rules" here, and the
temporary has to follow.)

And then comes the exception:

A temporary bound to a reference member in a
constructor’s ctorinitializer
(12.6.2) persists until the constructor exits.

So this seems to restrict the validity of the reference for this special case.

Therefore I believe we have a "special case" here.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26471