Const ref and rvalues again...

[martin]

Thanks Jonathan for the detailed info. So 'auto ref' is 
implemented the way I thought, by simply duplicating functions. 
That is actually the only way (I can think of) to solve your 
problem 'pass this argument in the most efficient way possible 
(do not copy)'.

But that is not the only problem. More commonly, we want to avoid 
copying lvalues for read-only parameters and therefore pass by 
reference. At the same time, we want to use the same function for 
rvalues - we simply can't stand having to declare temporaries 
manually or having to overload functions! Since the parameter is 
read-only, we couldn't care less if the argument is actually an 
lvalue or an rvalue. The only thing is that a dedicated function 
overload for rvalues would be slightly more efficient (for 
rvalues only) since the rvalue would be accessed directly on the 
stack instead of having to access it indirectly via its reference.
This problem here would be 'pass this argument as read-only in 
the most efficient way possible for lvalues (do not copy) but 
also allow rvalues at a slight cost (compared to a dedicated 
function overload)'.

So we do not really need 'auto ref' for non-templated functions 
or a new, even more confusing keyword which you, Jonathan, seem 
to insist on - 'const ref' (or, more elegantly 'in ref') is all 
we need. We simply want the compiler to automatically declare 
rvalues passed to 'const ref' parameters as local lvalues - 
problem solved for the majority of cases. For the remaining few 
which care about the involved cost for rvalue arguments, allow 
them to provide a function overload for rvalues (either manually 
or via 'auto ref' templates) - problem solved completely in my 
point of view. And that is actually exactly what the thread 
starter Malte proposes (and I already pointed that out in an 
earlier post).

Again hoping to be clear enough. :)