There's a need in generic code to have a function take a parameter by
ref if it is an lvalue, and by value if it is an rvalue. This can be
addressed by making it a template using auto ref:
T foo(T)(auto ref T x) { ... }
foo(3) // call by value
int y;
foo(y) // call by reference
There is also a need to 'transmit' the ref'ness to the return value.
This can be done with auto ref:
auto ref foo(T)(auto ref T x) { return x; }
foo(3) => int foo(int x)
foo(y) => ref int foo(ref int x)
This means that the generic forwarding function would look like:
auto ref foo(alias F, T...)(auto ref T args) { return F(args); }
