On Thursday, 14 March 2013 at 14:29:59 UTC, Andrea Fontana wrote:
On Thursday, 14 March 2013 at 13:58:56 UTC, monarch_dodra wrote:
On Thursday, 14 March 2013 at 13:20:51 UTC, Andrea Fontana
wrote:
On Thursday, 14 March 2013 at 12:29:26 UTC, Andrei
Alexandrescu wrote:
On 3/14/13 6:45 AM, Andrea Fontana wrote:
On Thursday, 14 March 2013 at 10:08:53 UTC, 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.
Add .save() to it.
Andrei
I can't add save and create a forward range: c-api doesn't
allow me to clone db cursor.
But think about it. You say you can't save, but you want pass
by value to preserve state. If you can preserve state, doesn't
that mean you just saved?
Once you've passed your "can't preserve state" to a foreach,
then your range is consumed. So yes, it is correct behavior.
Most input ranges should model reference semantics when
passed/copied by value. If somebody modifies the range, all
ranges are affected. The tough part is usually preserving
correct state.
I was hoping there's something I didn't know like rewind() to
implement :)
Ok, I'll pray db developer to add a clone method or I'll use
something like
auto res = cursor.array(); if needed
You *could* add rewind to your range, but it isn't quite the same
as save: Rewind means you can move back and forth in your view of
the file (or cursor/db), but it does not mean you can actually
*duplicate* (save) your range, to have two distinct ranges with a
distinct view of the your db.
For example, while the interface is different, a C "FILE*" is
what you'd call a rewindable input range with reference semantics.
