I don’t get the resistance to Dave’s solution? I think it works well and much
more applicable. Taking Susan’s original example, it’s not uncommon to want to
sort or filter by multiple mechanisms.
func byComparing<T, U: Comparable>(getComparisonKey: (T)->U) -> (T, T) -> Bool {
return { getComparisonKey($0) < getComparisonKey($1) }
}
struct Person {
var name: String
var age: Int
var height: Int
}
let peoples = [
Person(name: "Hawk", age: 24, height: 60),
Person(name: "Andrew", age: 23, height: 66)
]
let youngest = peoples.minElement(byComparing { $0.age })
let tallest = peoples.maxElement(byComparing { $0.height })
print("youngest: \(youngest?.name ?? "<none>")")
print("tallest: \(tallest?.name ?? "<none>")")
-David
> On Dec 31, 2015, at 8:19 AM, Dave Abrahams via swift-evolution
> <[email protected]> wrote:
>
>
>> On Dec 31, 2015, at 4:14 AM, Tino Heth <[email protected] <mailto:[email protected]>>
>> wrote:
>>
>>
>>> func byComparing<T, U: Comparable>(getComparisonKey: (T)->U) -> (T, T) ->
>>> Bool {
>>> return { getComparisonKey($0) < getComparisonKey($1) }
>>> }
>> I've written something similar to bring file URLs into the order of their
>> creation dates.
>> It is a small extension for collection types, and its only downside will
>> disappear as soon as properties are accessible via method calls (afair there
>> is a proposal in the making).
>>
>> It was quite a lot fiddling with generics, and I don't have the tiny piece
>> of code on my own computer, but it works in a way that you can do
>> let sorted = array.sortUsingAccessor(ElementType.methodThatReturnsComparable)
>> Beside the problems with properties, I really liked that approach.
>
> This seems to be essentially the same design as Susan’s, and has the same
> problem: it requires a new overload for every algorithm that takes a
> comparison predicate.
>
> -Dave
>
>
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