On Thursday, March 14, 2013 11:08:52 Andrea Fontana wrote:
> I'm trying to implement a db cursor as simple InputRange. I can't
> implement as forward range because using c-api I can't clone/save
> cursor.
>
> I wrote popFront() front() and empty() method and my range works
> fine.
>
> Using on a foreach() it browses all elements inside range until
> range is exausthed.
>
> If i do another foreach() it doesn't restart (empty() is called
> and it returns true, of course).
>
> Is it the correct behaviour of a inputrange or have i missed
> something?
foreach(e; range)
{
}
translates to something like
for(auto _range = range; !_range.empty; _range.popFront())
{
auto e = _range.front;
}
That means that foreach will alter the original range unless it's a struct
which implicitly saves via =. Pure input ranges can't be saved, and therefore
if you iterate over one until it's empty, it's empty, and it won't magically
have elements again if you use foreach on it again.
- Jonathan M Davis
