On Tuesday, 5 May 2015 at 02:47:03 UTC, bitwise wrote:
On Mon, 04 May 2015 00:16:03 -0400, Jonathan M Davis via
Digitalmars-d-learn <digitalmars-d-learn@puremagic.com> wrote:
D will move the argument if it can rather than copying it
(e.g. if a
temporary is being passed in), which reduces the need for
worrying about
copying like you tend to have to do in C++98, and I think that
a lot of D
code just doesn't worry about the cost of copying structs.
How exactly would you move a struct? Just a memcpy without the
postblit?
However, if you have a large object that you know is going to
be
expensive to copy, you're either going to have to use const ref
(and thus probably duplicate the function to allow rvalues), or
you're going to need to make it a reference type rather than
having all of its data live on the stack (either by making
it so that the struct contains a pointer to its data or by
making it a
class).
In general, if you're dealing with a type that is going to be
expensive to copy, I'd advise making it a reference type over
relying on
const ref simply because it's less error-prone that way. It's
trivial to
forget to use ref on a parameter, and generic code won't use
it, so it'll
generally work better to just make it a reference type.
- Jonathan M Davis
Something like a Matrix4x4 lives in an awkward place between a
class and a struct. Because of the fact that a graphics engine
may have to deal with thousands of them per frame, both copying
them at function calls, and allocating/collecting thousands of
them per frame, are both unacceptable.
I was reading up(DIP36, pull requests, forum) and it seems like
auto ref was supposed to do something like this. Is there a
reason you didn't mention it?
it does, auto ref can bind to both lvalues and rvalues. Create
the function with an empty template like so,
import std.stdio;
struct S{
}
void Foo()(auto ref S s){
}
void main(){
S s;
Foo(s);
Foo(S());
}
There might be other ways that I'm unaware of.
Why not just add "rvref" to D?
D is already bloated.
