08-Feb-2013 00:04, H. S. Teoh пишет:
On Thu, Feb 07, 2013 at 08:40:25PM +0100, Peter Alexander wrote:
[...]
1) To avoid excessive allocations, it would have to be a transient
range. Which means it may have unexpected results if you use it with
an algorithm that doesn't handle transient ranges correctly.
This has been discussed previously. bearophile suggested a policy to
control whether the buffer is permuted in-place, with it defaulting
to creating duplicates. The slow down from duplicates on DMD was
~3x.
Hmm. There's also the problem that there is no generic way to duplicate
a range. Only arrays are guaranteed to support .dup and .idup. So you'd
have to allocate an array to store each permutation, and return that
instead of the original range. This could be a major problem (one might
expect to get elements of the same type as the original range, instead
of arrays!).
I had long thougth of primitive like:
build!Container(range);
And if Container is not important then this :
build(range); //okay here build might be worse then dup
and it peeks the right container inside of it based on power of range
Such as:
random access - deque (or array)
forward - unrolled s-list (or deque)
bidirectional - deque
After typing this it seems like Phobos is in dire need of deque ;)
--
Dmitry Olshansky
