Hi Gwendal, these are use cases for using indices as unordered references which
certainly are useful. I was looking for use cases depending on the order
exposed by Sequence, specifically use cases for elementsEqual.
-Thorsten
> Am 17.10.2017 um 09:03 schrieb Gwendal Roué <gwendal.r...@gmail.com>:
>
>>> Modeling is, by definition, imperfect. The question is, what imperfect
>>> model is most useful _to Swift_. The idea is that conforming Set and
>>> Dictionary to Collection is on balance more useful than not doing so; that
>>> having two protocols, Sequence and Collection, is on balance more useful
>>> than having one or three, and that the set of semantic guarantees of
>>> Collection are on balance more useful than other possible sets of semantic
>>> guarantees.
>>
>> That is your idea which is disputed and underlined with arguments whereas
>> you keep repeating that Set behaves as dictated by its conformance without
>> giving use cases why this should be useful.
>
> Hello,
>
> You can't *control* the ordering of a set or a dictionary, but you can still
> *rely* on it.
>
> For example, to find a key in a dictionary that is associated a given value,
> you can rely on the fact that a dictionary's order is guaranteed to be
> stable, and that on top of that its indexes can address the dictionary
> itself, but also its keys and values sequences. The code below has no bug;
>
> let dict = ["a": "foo", "b": "bar", "c": "needle"]
>
> // Find a key associated with "needle"
> if let index = dict.values.index(of: "needle") {
> let key = dict.keys[index]
> print(key) // prints "c"
> }
>
> It's more difficult to find a use case for set's ordering and indexes. But
> since you ask, here is an example. The goal is to find any element which is
> not equal to another value, in any collection:
>
> extension Collection where Element: Equatable {
> /// Returns any element which is not equal to the given element
> func anyElement(notEqualTo v: Element) -> Element? {
> if let i = index(of: v) {
> if let alt = index(i, offsetBy: 1, limitedBy: endIndex), alt !=
> endIndex {
> return self[alt]
> }
> if i == startIndex {
> return nil
> }
> return first
> }
> return first
> }
> }
>
> Set([1, 2, 3]).anyElement(notEqualTo: 1) // 2 or 3
> Set([1, 2]).anyElement(notEqualTo: 1) // 2
> Set([1]).anyElement(notEqualTo: 1) // nil
> Set([2]).anyElement(notEqualTo: 1) // 2
> Set([]).anyElement(notEqualTo: 1) // nil
>
> That *can* be useful, isn't it?
>
> Gwendal Roué
>
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