On Wednesday, 31 December 2014 at 05:28:31 UTC, Andrei
Alexandrescu wrote:
The alternate hypothesis is "ref" is being misused. "ref" is
for propagating changes into the arguments. It should be rare
that code does not actually care for that. Unlike in C++, ref
is seldom needed for optimizing copies away. -- Andrei
Could you elaborate on that? Say I've got some big, expensive
struct I want to pass into a function efficiently. In C++ I'd do
this by const reference (or reference if I'm making changes).
What does D do that would make the ref unnecessary for
efficiency? I can't imagine the compiler doing any sort of copy
(even the efficient blig) being as fast as just passing in a
reference. There is also a problem if the struct has disabled
postblit. If the compiler silently turned something passed by
value into a secret reference then it would open the door for
problems during multithreading.
It is a shame that there is a conflation between an optimization
and a tool for more flexible code structure. It makes it hard to
express your intention when you use ref.
With DIP25 it seems like passing in an rvalue by ref would be
safer and thus open it to being allowed.
