On Friday, 26 April 2013 at 10:33:17 UTC, Timon Gehr wrote:
On 04/26/2013 01:58 AM, Zach the Mystic wrote:
But as
you said, figuring out the rules for making the compiler smart
enough to
choose the right one seems like a hard task.
I think it is easy.
If it forwards to another
'auto ref' template parameter, it needs to descend into that
template,
determine *its* type of parameter, and then assign the type of
its own
parameter accordingly.
...
No, when forwarding to another template, non-lazy parameters
will always have an address, ref or not ref.
This suggestion simplifies the problem greatly. Is the suggestion
made precisely because it simplifies the problem, or do you also
consider it better with regard to performance and safety?
The cases where it makes a difference are auto ref returns,
__traits(isRef, ...), and lazy auto ref parameters. (If there
are more, they will be detected by grepping the compiler source
for occurrences of the 'ref' "storage class" representation,
presumably an enum value.)
The compiler does not have to be particularly smart. IMO this
is the way to generalize auto ref to non-template functions.
I think it's useful to realize that if the end result of an
action is the same, it's not necessary to know exactly how the
compiler solved the problem. If both creating a temporary, and
passing the argument to its own template-instantiated function
produce the same semantics, then to some extent it doesn't matter
how the compiler did it. That leaves the question of performance.
If it were demonstrated that neither mechanism outperforms the
other, then it *really* doesn't matter which it chooses.
