[swift-evolution] Nested for-in loops syntax

Nevin Brackett-Rozinsky nevin.brackettrozinsky at gmail.com
Sun Jul 17 10:54:56 CDT 2016

I think this use-case is too narrow for dedicated syntax in the standard

However, it should be simple enough for you to write your own function,
let’s call it `unpack`, which produces a sequence that does what you want.

While you’re at it you could also try writing a `cross` function that takes
two collections and produces all tuples of their elements, perhaps using
something like .lazy.map.zip internally, if you need that functionality.

One great aspect of Swift is that it makes implementing things like this
yourself readily achievable. Plus, once we get constrained extensions
(extension Collection where Element: Collection) you should be able to do
it that way too.

Alternatively, you might consider whether your data structure itself is
ideal or if you’d be better off flattening everything into, say, a single
dictionary that takes a compound key.


On Sun, Jul 17, 2016 at 6:05 AM, Maxim Bogdanov via swift-evolution <
swift-evolution at swift.org> wrote:

> Hello, community.
> As I understood from documentation the only way to iterate
> multidimensional array or a dictionary (with for loop) is this:
> let multidimensionalDictionary = ["a":["b": "c"], "b":["c": "d"], "c":
> ["d": "e"]]
> for (key, value) in multidimensionalDictionary {
>     for (nestedKey, nestedValue) in value {
>         print("\(key) -> \(nestedKey) -> \(nestedValue)")
>     }
> }
> What do you think about this syntax?
> for (key, nestedKey, nestedValue) in multidimensionalDictionary {
>     print("\(key) -> \(nestedKey) -> \(nestedValue)")
> }
> --
> I'm new to mailing list feature. If I do something wrong please let me
> know about it.
> Best regards,
> Maxim
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> swift-evolution mailing list
> swift-evolution at swift.org
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