On Tuesday, 3 July 2012 at 17:40:24 UTC, Jonathan M Davis wrote:
On Tuesday, July 03, 2012 17:31:21 Christophe Travert wrote:
takeFront implementation is dangerous for ranges which
invalidates their
front value when popFront is called, for instance,
File.byLine. Thus
takeFront will have to be used with care: any range implement
takeFront
(because of the template and USFC), but it may not be valid.
That makes
the range interface more complicated: There is a takeFront
property, but
you have to check it is safe to use... how do you check that
by the way?
Hmm. I hadn't thought of that. That could be a good reason not
to do this. I'm
not quite sure how to get around that. Hmmm... It would
arguably be a bit
ugly, but a range which couldn't safely be used with takeFront
could have an
enum on it which indicated that, and takeFront would fail to
compile if used
with such a range. Of course, that would mean that you'd have
to special case
such ranges in any range-based function which used takeFront so
that there was
a branch which didn't use takeFront for ranges which couldn't
use it.
Just an idea (feels dirty, but still): such range could redefine
takeFront, and maintain state. takeFront would defer a call to
popFront until the next operation. All of front, popFront,
takeFront and empty would check state (whether popFront has been
deferred), and execute popFront first. Side effect would be that
a call to empty would invalidate result of takeFront, but that
could be changed also: empty instead of calling popFront would
check whether there is anything else after the front element.
This is much more complicated, but would only be necessary for
such containers.
