Re: operator class&() { return *this; } considered harmful?

Alberto Ganesh Barbati wrote:
 > Michael Norrish ha scritto:
 >> Clearly, the rvalue reference proposal solves all sorts of other
 >> interesting issues apart from the one in my example, but my question
 >> is really whether or not
 >>
 >> operator C&() { return *this; }
 >>
 >> will safely achieve what I want.
 >>
 >
 > I don't think so. According to my interpretation, 12.2/5 doesn't apply
 > here, because in line:
 >
 > C &x = f();
 >
 > the reference x is *not* bound to a temporary, but rather to the result
 > of the call to operator C& which is a reference (such reference
 > *happens* to be bound to a temporary but this fact is irrelevant to a
 > strict interpretation of 12.2/5).
 >
 > I expect the temporary to be properly destroyed at the end of the
 > full-expression, making x a dangling reference.

If this is so, is there any point to the language in 8.5.3/5 allowing
this? (This language is "if the initializer expression ... has a
class type ... and can be implicitly converted to an lvalue....". The
footnote emphasises that this situation can only arise when you have a
conversion function returning a reference type.)

That clause only applies when the initialisor is not an lvalue, so
there will be a temporary here anyway. That temporary can only get
turned into an l-value via a conversion function, but if you are
right, then the conversion function can't usefully return a reference
to the temporary it's called on because that temporary will disappear
as soon as the declaration of the reference completes. (The
conversion function could return a reference to something other than
the temporary of course; some global perhaps).

Michael.

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