Move semantics for D

[monarch_dodra]

On Friday, 13 July 2012 at 09:47:26 UTC, Jonathan M Davis wrote:
> On Friday, July 13, 2012 11:23:41 monarch_dodra wrote:
>> I think that in the case of your example, if "range" fulfills 
>> the
>> requirements for (at least) an input range, then "save" 
>> *should*
>> be called instead of "opSlice". I'm *think* this is what the
>> compiler does, but I'm not 100% sure.
>
> The compiler never calls save. It will call opSlice on 
> non-ranges, but it'll
> never call save on anything. It doesn't even know that save 
> exists. It's
> unnecessary for ranges which aren't reference types, and you 
> already have to
> worry about calling save on ranges that could be reference 
> types any time that
> you pass them to a function that you don't want to consume it, 
> so it's not
> really a big deal to have to call save with foreach for such 
> ranges. Most
> range-based functions don't even use foreach much anyway.
>
> - Jonathan M Davis

What exactly are the semantics of save? The reference in 
std.range isn't very clear. It would appear it is only useful it 
its *existence* that promotes a range from input to forward. 
However, how is it different from a simple assignment?

Also, if you are supposed to call save before a foreach 
"consumes" your range, then why does foreach even bother making a 
copy of the range before iterating on it? Isn't this behavior 
promoting dangerous usage for ranges where save is simply 
"{return this;}", but bites you in the ass the day you use a 
range with a specific save?

I'm confused...