[phobos] phobos commit, revision 2270

[Andrei Alexandrescu]

The problem is you either need to add a Boolean flag "backWasComputed" 
or two for completeness. The problem is, often checking the flag every 
time you access front or back may be almost as expensive as the 
filtering operation itself.

I reached the belief that the canonical filter() implementation should 
have absolutely no surprise: no flags, no caching, no frills. Just one 
test per container element. So that precludes it being bidirectional. 
The bidirectional filter is equally unsurprising.


Andrei

On 1/3/11 12:00 PM, David Simcha wrote:
> Why is this a speed disadvantage?  IMHO, filterBidirectional should be
> the only flavor of filter.  Either way, exactly one complete pass has to
> be made through the base range to iterate over the Filter.  It just
> means that things will be computed slightly more eagerly.  Are there any
> very important use cases where this is a major disadvantage?
>
> On Mon, Jan 3, 2011 at 12:54 PM, dsource.org <http://dsource.org>
> <noreply at dsource.org <mailto:noreply at dsource.org>> wrote:
>
>     phobos commit, revision 2270
>
>
>     user: andrei
>
>     msg:
>     Added filterBidirectional for completeness
>
>     http://www.dsource.org/projects/phobos/changeset/2270
>
>     paths changed:
>     U   trunk/phobos/std/algorithm.d
>
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