Jason House wrote:
Andrei Alexandrescu wrote:
Philippe Sigaud wrote:
On Thu, Dec 31, 2009 at 16:47, Michel Fortin <[email protected]
<mailto:[email protected]>> wrote:
On 2009-12-31 09:58:06 -0500, Andrei Alexandrescu
<[email protected]
<mailto:[email protected]>> said:
The question of this post is the following: should output ranges
be passed by value or by reference? ArrayAppender uses an extra
indirection to work properly when passed by value. But if we
want to model built-in arrays' operator ~=, we'd need to request
that all output ranges be passed by reference.
I think modeling built-in arrays is the way to go as it makes less
things to learn. In fact, it makes it easier to learn ranges because
you can begin by learning arrays, then transpose this knowledge to
ranges which are more abstract and harder to grasp.
I agree. And arrays may well be the most used range anyway.
Upon more thinking, I'm leaning the other way. ~= is a quirk of arrays
motivated by practical necessity. I don't want to propagate that quirk
into ranges. The best output range is one that works properly when
passed by value.
I worry about a growing level of convention with ranges. Another recent
range thread discussed the need to call consume after a successful call to
startsWith. If I violated convention and had a range class, things would
fail miserably. There would be no need to consume after a successful call
to startsWith and the range would have a random number of elements removed
on an unsuccessful call to startsWith. I'm pretty sure that early
discussions of ranges claimed that they could be either structs and classes,
but in practice that isn't the case.
I am implementing right now a change in the range interface mentioned in
http://www.informit.com/articles/printerfriendly.aspx?p=1407357, namely:
add a function save() that saves the iteration state of a range.
With save() in tow, class ranges and struct ranges can be used the same
way. True, if someone forgets to say
auto copy = r.save();
and instead says:
auto copy = r;
the behavior will indeed be different for class ranges and struct ranges.
Andrei
