On Tue, 18 Jan 2011 01:11:04 -0500, Andrei Alexandrescu
<[email protected]> wrote:
On 1/17/11 11:48 PM, Jonathan M Davis wrote:
On Monday 17 January 2011 15:13:42 spir wrote:
See range bug evoked above. opApply is the only workaround AFAIK.
Also, ranges cannot yet provide indexed iteration like
foreach(i, char ; text) {...}
While it would be nice at times to be able to have an index with
foreach when
using ranges, I would point out that it's trivial to just declare a
variable
which you increment each iteration, so it's easy to get an index even
when using
foreach with ranges. Certainly, I wouldn't consider the lack of index
with
foreach and ranges a good reason to use opApply instead of ranges.
There may be
other reasons which make it worthwhile, but it's so trivial to get an
index that
the loss of range abilities (particularly the ability to use such
ranges with
std.algorithm) dwarfs it in importance.
- Jonathan M Davis
It's a bit more difficult than that. When iterating a variable-length
encoded range, what you need more than the current item being iterated
is the physical offset reached inside the range. That's not all that
difficult either as the range can always provide an extra primitive, but
a bit annoying (e.g. because it makes iteration with foreach impossible
if you want the index, unless you return a tuple with each step).
At any rate, I agree with two things - one, we need to fix the foreach
situation. Two, even before we find a fix, at this point committing to
iteration with opApply essentially commits the iteratee to an island
where all basic algorithms need to be reinvented from first principles.
opApply in no way disables the range interface. It simply is used for
foreach. So the only "algorithm" which is different is foreach. If you
use the range primitives, opApply is nowhere to be found.
That being said, we have an annoying situation in all this. opApply
cannot be used to foreach using indexes *and* ranges are used to foreach
elements. If one opApply is found, the compiler gives up on using the
range functions for foreach (this is reflected in my most recent string_t
code). This means you will have to implement a "wrapper" opApply around
the range primitives in order to also implement indexing foreach.
-Steve
