Rvalue references - The resolution

[Andrei Alexandrescu]

On 5/6/13 12:48 PM, Steven Schveighoffer wrote:
> On Mon, 06 May 2013 06:43:38 -0700, Andrei Alexandrescu
> <SeeWebsiteForEmail at erdani.org> wrote:
>
>> I think we can technically make the overloading work while also
>> allowing binding rvalues to ref. But that wouldn't help any. Consider:
>>
>> ref int min(ref int a, ref int b) { return b < a ? b : a; }
>> ...
>> int x;
>> fun(min(x, 100));
>>
>> Here the result of min may be bound to an lvalue or an rvalue
>> depending on a condition. In the latter case, combined with D's
>> propensity to destroy temporaries too early (immediately after
>> function calls), the behavior is silently undefined; the code may pass
>> unittests.
>
> Wouldn't the new runtime check fix this?

Depends how you define "fix". It would be a possibly rare bounds check 
violation on completely innocuous code.

>> This is a known issue in C++. Allowing loose binding of rvalues to ref
>> not only inherits C++'s mistake, but also adds a fresh one.
>
> I thought C++ would handle this kind of code. I remember being able to
> use references to rvalues in ways that were unintuitive, but not undefined.

template <class T> const T& min(const T& a, const T& b) {
     return b < a ? b : a;
}
...
int x = ...;
auto & weird = min(x, 100);

Have a nice day :o).


Andrei