improving the join function

[Philippe Sigaud]

On Tue, Oct 12, 2010 at 03:28, Simen kjaeraas <simen.kjaras at gmail.com> wrote:
> Daniel Gibson <metalcaedes at gmail.com> wrote:
>
>> (*) Something like
>> Range!(Tuple!(T1, T2)) join(T1, T2)(Range!(T1) r1, Range!(T2) r2,
>> BinaryPredicate!(T1, T2) joinPred)
>> just pseudo-code, I'm not really familiar with D2 and std.algorithm.
>> The idea is you have a Range r1 with elements of type T1, a Range r1 with
>> elements of type T2 and a predicate that gets a T1 value and a T2 value and
>> returns bool if they match and in that case a Tuple with those two values is
>> part of the Range that is returned.
>
> Once again I see the combinatorial range in the background. Man, why does
> this have to be so hard?
>
> That is, your join could be implemented as follows, given the
> combinatorial product range combine:
>
>
> auto join( alias fun, R... )( R ranges ) if ( allSatisfy!( isForwardRange, R
> ) ) {
>    return filter!fun( combine( ranges );
> }

And IIRC, there is a difference between outer join, inner join and
some other versions.
So

filter!fun(zip(ranges))

(that is, filtering in parallel) is also a possibilty. I should read
some again on DB joints.
There is also the need for creating a range of ranges on this one
(aka, tensor product, but that scares people when I say that)
Anyway, that's derailing the thread, so I'll stop now.