Re: Template argument as rvalue reference
Am 26.10.2012 13:20, schrieb Juha Nieminen:
SG <sgesemann@gmail.invalid> wrote:
No, reference collapsing is always applicable. It is not restricted to
the case of templates.
I think it is.
Then you are wrong. Or perhaps you have a different idea about what
"reference collapsing" means.
If you have a non-templated rvalue reference parameter,
you can't give it an lvalue. You'll get a compile error.
What is an "rvalue reference parameter"?
typedef int& foo;
void bar(foo&& x);
void test() {
int a = 23;
bar(a); // actually works
}
Is x of bar an rvalue reference parameter? Well, it looks like one. But
it is not. Due to reference collapsing x is actually an lvalue
reference. This is reference collapsing outside of the context of
templates. Please don't confuse reference collapsing with template
argument deduction.
The only situation where an rvalue reference is automatically collapsed
to a regular reference is with templates.
I think you're mixing two different things: reference collapsing and
template argument deduction. The former has nothing to do with templates.
template<typename T> void foo(T&&, T&&);
This is not the way to enable perfect forwarding.
How is that relevant to my question?
I dunno. Maybe you're trying to do/understand perfect forwarding. At
least it's the main reason why anybody would use T&& as function
parameter type where T is deduced. In that case, the information that
T&& should only be used for one parameter is useful.
Cheers!
SG