On Tuesday, 2 June 2015 at 18:05:20 UTC, Namespace wrote:
AFAIK Andrei wanted 'auto ref' as the syntax which accepts
both, lvalues and rvalues. That's why I'm asking if the current
behaviour for auto ref for templates should change, or not. If
not, we have (as you said) two meanings of auto ref, what is
not optimal, but not so bad either (IMO).
But if I had the choice, I would change it for both, so that
both create a temporary variable for rvalues.
Andrei originally wanted auto ref to apply to non-templated
functions, but Walter misunderstood what he meant and created
what we have now - which is actually incredibly useful, because
it allows you to forward the attributes of an argument - in
particular, it's ref-ness. So, we definitely do _not_ want to
lose that.
So, basically, I think that we have three options:
1. Do nothing. If you want a function parameter to accept both
lvalues and rvalues efficently, then either duplicate it with
various overloads to achieve that or templatize it and use
auto ref so that the compiler will do that for you.
But that means we get (at worst) 2^N functions. And note that
each function contains the whole body, not just a call to one
of the previous creations.
Yes. auto ref with templated functions results in a lot of
template bloat if you use it heavily, which is part of why using
auto ref with non-templated functions at this point isn't a
particularly ideal solution, not unless we could actually make it
so that the compiler could optimize the extraneous instantiations
and use a temporary value for the rvalues when the attribute
forwarding isn't actually needed, but I wouldn't really expect us
to get that.
- Jonathan M Davis
