On Sunday, 23 March 2014 at 00:50:34 UTC, Walter Bright wrote:
It's become clear to me that we've underspecified what an
InputRange is. The normal way to use it is:
while (!r.empty) {
auto e = r.front;
... do something with e ...
r.popFront();
}
no argument there. But there are two issues:
1. If you know the range is not empty, is it allowed to call
r.front without calling r.empty first?
If this is true, extra logic will need to be added to r.front
in many cases.
2. Can r.front be called n times in a row? I.e. is calling
front() destructive?
If true, this means that r.front will have to cache a copy in
many cases.
Is InputRange supposed to be a one-pass range and am I supposed
to able to use InputRange as a lightweight wrapper for a stream?
If the answer is yes, then I think the fundamental issue is that
the empty-front-popFront interface is not optimal for something
like InputRange. But given that's the interface we have, I think
that InputRange's front must be allowed to be destructive because
the stream it could potentially be wrapping is destructive.
