Should range foreach be iterating over an implicit copy?

[Era Scarecrow]

On Wednesday, 16 May 2012 at 21:37:54 UTC, Nick Sabalausky wrote:
> A small debate has broken out over on D.learn (
> http://forum.dlang.org/thread/jovicg$jta$1@digitalmars.com#post-jovicg:24jta:241:40digitalmars.com 
> )
> that I thought I should move here.
>
> Basically, the issue is this: Currently, when you have a 
> struct-based range, foreach will iterate over a *copy* of it:

http://forum.dlang.org/post/dskrijudairkopeoyqkc@forum.dlang.org

I've replied in the other one, but I'll repost it here, perhaps 
andrei can correct me.

---

On Wednesday, 16 May 2012 at 20:50:55 UTC, Nick Sabalausky wrote:

> I was initially open to the idea I may have just misunderstood 
> something, but I'm becoming more and more convinced that the 
> current "foreach over an implicit copy" behavior is indeed a 
> bad idea.
>
> I'd love to see Andrei weigh in on this. I'm curious if the 
> example you pointed out in TDPL made the copy deliberately, or 
> if the effects of that copy were just an oversight.

  I remember going over hard and long over that section. I think 
it's deliberate.

  Range can refer to many things, and I'm assuming array is one of 
them. So... If the array is consumed when using foreach, that 
seems dumb right? (An array in the end is just a small struct 
afterall...)

---
int[] x = [1,2,3];
foreach(i; x) {
  //stuff
}

  assert(x.length == 0, "Should have been consumed!");
---

  Structs being value types are by value and so are copied, not 
referenced. Although referencing a copy does seem a bit silly...

int[] x = [1,2,3];
foreach(ref i; x) {
  i = 10;
}

assert(x == [10,10,10], "But i changed them to 10!!");

--

  That means that foreach(ref; ref) if it's considered (And I 
think it makes sense to) would work for structs in these few 
cases. (Course you'd still consume dynamic arrays that way)

  In std.stream are classes, so they are consumed. I'm probably 
just rambling...