[swift-evolution] sortBy, minElementBy and maxElementBy methods

[Susan Cheng]

It confuses people if provide a global function byComparing in stdlib
which's doing nothing alone.

Dave Abrahams <dabrahams at apple.com> 於 2015年12月31日星期四 寫道：

> Why add all those algorithms when you can write this
>
> func byComparing<T, U: Comparable>(getComparisonKey: (T)->U) -> (T, T) ->
> Bool {
>   return { getComparisonKey($0) < getComparisonKey($1) }
> }
>
> peoples.sort(byComparing { $0.name })
>
> ?
>
> -Dave
>
> On Dec 30, 2015, at 10:38 PM, Susan Cheng via swift-evolution <
> swift-evolution at swift.org
> <javascript:_e(%7B%7D,'cvml','swift-evolution at swift.org');>> wrote:
>
>
> Consider the follows:
>
> struct Person {
>
>
>     var name: String
>     var age: Int
> }
>
> let peoples = [Person(name: "Hawk", age: 24), Person(name: "Andrew", age:
> 23)]
>
> let youngest = peoples.minElement { $0.age < $1.age }
>
> print(youngest?.name)
>
> it's silly that we always have to write the code like { $0.some < $1.some }
> or { some($0) < some($1) }
>
> so, we should add those methods to stdlib:
>
> extension SequenceType {
>     /// Returns the minimum element in `self` or `nil` if the sequence is
> empty.
>     ///
>     /// - Complexity: O(`elements.count`).
>     ///
>     @warn_unused_result
>     public func minElement<R : Comparable>(@noescape by:
> (Generator.Element) throws -> R) rethrows -> Generator.Element? {
>         return try self.minElement { try by($0) < by($1) }
>     }
>     /// Returns the maximum element in `self` or `nil` if the sequence is
> empty.
>     ///
>     /// - Complexity: O(`elements.count`).
>     ///
>     @warn_unused_result
>     public func maxElement<R : Comparable>(@noescape by:
> (Generator.Element) throws -> R) rethrows -> Generator.Element? {
>         return try self.maxElement { try by($0) < by($1) }
>     }
> }
>
> public extension MutableCollectionType {
>
>
>     /// Return an `Array` containing the sorted elements of `source`.
>     /// according to `by`.
>     ///
>     /// The sorting algorithm is not stable (can change the relative
> order of
>     /// elements that compare equal).
>     @warn_unused_result(mutable_variant="sortInPlace")
>     func sort<R : Comparable>(@noescape by: (Generator.Element) -> R) -> [
> Generator.Element] {
>         return self.sort { by($0) < by($1) }
>     }
> }
>
> public extension MutableCollectionType where Self.Index :
> RandomAccessIndexType {
>
>
>     /// Sort `self` in-place according to `by`.
>     ///
>     /// The sorting algorithm is not stable (can change the relative
> order of
>     /// elements that compare equal).
>     mutating func sortInPlace<R : Comparable>(@noescape by: (Generator.
> Element) -> R) {
>         self.sortInPlace { by($0) < by($1) }
>     }
> }
>
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> <javascript:_e(%7B%7D,'cvml','swift-evolution at swift.org');>
> https://lists.swift.org/mailman/listinfo/swift-evolution
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.swift.org/pipermail/swift-evolution/attachments/20151231/b444c20e/attachment.html>