refRange with non copyable struct

[Jonathan M Davis via Digitalmars-d-learn]

On Monday, April 17, 2017 18:45:46 Jerry via Digitalmars-d-learn wrote:
> On Monday, 17 April 2017 at 18:07:36 UTC, Jonathan M Davis wrote:
> > In this particular case, it looks like the main problem is
> > RefRange's opAssign. For it to work, the type needs to be
> > copyable. It might be reasonable for RefRange to be enhanced so
> > that it doesn't compile in opAssign if the range isn't
> > copyable, but I'd have to study RefRange in depth to know what
> > the exact consequences of that would be, since it's been quite
> > a while since I did anything with it. My guess is that such a
> > change would be reasonable, but I don't know without studying
> > it.
> >
> > - Jonathan M Davis
>
> I took a look on RefRange and the reasoning is clearly explained
> in the docs like this:
>
> This does not assign the pointer of $(D rhs) to this $(D
> RefRange).
> Rather it assigns the range pointed to by $(D rhs) to the range
> pointed
> to by this $(D RefRange). This is because $(I any) operation on a
> RefRange) is the same is if it occurred to the original range. The
> exception is when a $(D RefRange) is assigned $(D null) either
> or because $(D rhs) is $(D null). In that case, $(D RefRange)
> longer refers to the original range but is $(D null).
>
>
>
> But what I do not understand is why this is important.

Because otherwise, it's not acting like a reference to the original range,
which is the whole point of RefRange. The correct solution would probably be
to @disable opAssign in the case where the original range can't be
overwritten by another range.

- Jonathan M Davis