Here's what I ended up with. (The use-case for this ended up being light-weight
game tile placement, not image processing or anything. )
func cartesianProduct<S1: SequenceType, S2: SequenceType>(s1: S1, _ s2: S2) ->
AnySequence<(S1.Generator.Element, S2.Generator.Element)> {
let items = s1.lazy.flatMap({
item1 in s2.lazy.map({
item2 in (item1, item2)})})
return AnySequence {items.generate()}
}
func cartesianProduct<S1: SequenceType, S2: SequenceType, S3: SequenceType>(s1:
S1, _ s2: S2, _ s3: S3) -> AnySequence<(S1.Generator.Element,
S2.Generator.Element, S3.Generator.Element)> {
let items = s1.lazy.flatMap({
item1 in s2.lazy.flatMap({
item2 in s3.lazy.map({
item3 in (item1, item2, item3)})})})
return AnySequence {items.generate()}
}
I initially suggested to the person I was helping:
for y in (...) {
for x in (...) {
...
}
}
But I'm glad I got to explore several alternative approaches. Thanks all. A few
extra notes, to summarize everything into a single post:
Joe writes: "[AnySeq/Gen] aren't on the way out. We'd like to migrate them with
first-class language support for protocol types with associated type
constraints, but we wouldn't eliminate the functionality."
Dmitri adds: "You can use AnySequence and AnyGenerator, but they come at a cost
of dynamic dispatch for every call. In this case, if you want this component
to be suitable for performance-critical code, I would suggest to avoid them for
now."
-- E
> On Dec 18, 2015, at 11:08 PM, Rob Mayoff via swift-users
> <swift-users@swift.org> wrote:
>
> 1. Can anyone recommended a better name than Cartesian? 2D doesn't work for
> the compiler and I'm looking for something that doesn't seem
> "floating-point"-y
>
> "AllPairs" seems self-explanatory.
>
> "CrossJoin" should be intuitive to anyone familiar with relational databases.
>
> "product" sounds like it might be multiplying elements with each other.
>
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