More on "Component Programming"

[Timothee Cour]

On Mon, May 27, 2013 at 9:53 PM, H. S. Teoh <hsteoh at quickfur.ath.cx> wrote:

> On Mon, May 27, 2013 at 09:24:28PM -0700, Timothee Cour wrote:
> > > Done, turns out the fix was trivial, just swapping two static ifs:
> > > https://github.com/D-Programming-Language/phobos/pull/1314
> >
> > This isn't what Andrei had in mind in his post above:
> >
> > > I'm disappointed cartesianProduct works that way; I should have
> > > caught that during the code review. A better iteration order would
> > > have spanned the lower position in both ranges first, i.e. create
> > > squares of increasing side in the 2D space.
> >
> > I would suggest an additional template parameter to specify the order
> > of iteration:
> [...]
>
> The problem with allowing the user to specify order is that when one or
> more of the input ranges are infinite, the order of traversal is much
> less flexible, and it may not be possible to satisfy the requested
> order.
>

Explicit is better than implicit. The user should request the order, and
the compiler can statically disallow
lexicographic_depth/antilexicographic_depth
when at least one of the ranges is infinite.


>
> The order that Andrei suggested is what's currently used for two
> infinite ranges, though when finite ranges are involved I chose a
> slightly simpler implementation. The order bearophile proposed in issue
> 9878 is different from what Andrei describes, at any rate.
>
> What's the typical output order of cartesian products in other languages
> / libraries? It seems nobody can agree on what the order should be. :-/
>
>
python uses itertools.product which is lexicographic_depth.
Like you say, no-one can agrees what the order should be, so let's leave it
up to user through a template. Sounds like a no-brainer to me. There are
use cases for each order I mentioned.


>
> T
>
> --
> People demand freedom of speech to make up for the freedom of thought
> which they avoid. -- Soren Aabye Kierkegaard (1813-1855)
>
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