> On 17 Feb 2017, at 01:26, Ben Cohen via swift-evolution
> <[email protected]> wrote:
>
> Here is a list of commonly requested changes/enhancements to Dictionary, all
> of which would probably be appropriate to put together into a single
> evolution proposal:
>
> init from/merge in a Sequence of Key/Value pairs (already raised as SE-100:
> https://github.com/apple/swift-evolution/blob/master/proposals/0100-add-sequence-based-init-and-merge-to-dictionary.md
>
> <https://github.com/apple/swift-evolution/blob/master/proposals/0100-add-sequence-based-init-and-merge-to-dictionary.md>).
> make the Values view collection a MutableCollection (as in this PR:
> https://github.com/apple/swift-evolution/pull/555
> <https://github.com/apple/swift-evolution/pull/555>).
> Add a defaulting subscript get (e.g. counts[key, default: 0] += 1 or
> grouped(key, default:[]].append(value)).
> Add a group by-like init to create a Dictionary<K,[V]> from a sequence of V
> and a closure (V)->K.
Out of interest, how would you implement this? Does it require a generics
feature that's slated for Swift 4? I tried two approaches that don't compile in
a current Swift 3.1 snapshot (and I'm getting a segfault with both examples in
a dev snapshot from 2017-02-14):
1)
extension Dictionary {
// error: same-type constraint 'Value' == '[S.Iterator.Element]' is
recursive
init<S: Sequence>(values: S, groupedBy: (S.Iterator.Element) -> Key)
where Value == [S.Iterator.Element] {
...
}
}
}
2)
// error: reference to generic type 'Array' requires arguments in <...>
extension Dictionary where Value == Array {
init<S: Sequence>(values: S, groupedBy: (S.Iterator.Element) -> Key)
where S.Iterator.Element == Value.Element {
...
}
}
}
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