[swift-evolution] sortBy, minElementBy and maxElementBy methods

[Dave Abrahams]

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> 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) }
>     }
> }
> 
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