Map Sorting

Evolution Pitches
20

I think it may be useful to have real-world statistics on how often < , > , and other more complicated sorting constructs ( localizedCaseInsensitiveCompare == .orderedAscending is my go-to "complex" example) actually get used in the wild.

In the Swift Source Compatibility Suite

I identified 243 instances of sort / sorted in the swift-source-compat-suite. Of these 243, 80% (194) used < either as their comparator or as the primary operation in their comparator closure. 12% (30) used >. The remaining 8% of sorts (19) mostly checked for == .orderedAscending. Only 1-2% of the sorts in the compatibility suite used some comparison operator other than <, > or == .orderedAscending.

54% (132) of the sorts provided a custom areInIncreasingOrder closure. Of those 132 closures, 53% (71) took the form { $0.someProperty < $1.someProperty } and 10% (14) took the form { $0.someProperty > $1.someProperty }.

Potential Impact of this Proposal

In all, 30% of the sorts I identified in the Source Compatibility Suite took the form { $0.someProperty < $1.someProperty }. Over half of the sorts that provided a custom areInIncreasingOrder closure took that form as well.

With these overloads below, 30% of all sorts in the compatibility suite (and the majority of sorts that provided a areInIncreasingOrder closure at all) could be improved from sorted { $0.someProperty < $1.someProperty } to sorted { $0.someProperty }.

5% could be improved from sorted { $0.someProperty > $1.someProperty } to sorted(using: { $0.someProperty }, by: >)

extension Sequence {
    func sorted<Value>(using transform: (Element) -> Value, by: (Value, Value) -> Bool) -> [Element] {
        ...
    }
    
    func sorted<Value: Comparable>(using transform: (Element) -> Value) -> [Element] {
        return self.sorted(using: transform, by: <)
    }
}

// + corresponding `sort` overloads

My raw notes:

.sorted(): 62
.sort(): 7
.sorted(by: <): 30
.sort(by: <): 0

.sorted(by: >): 12
.sort(by: >): 0

.sorted {
total: 87
block with <: 67
block with >: 8
{ $0.someProperty < $1.someProperty }: 48
{ $0.someProperty > $1.someProperty }: 6

.sorted(by: {
total: 36
block with <: 24
block with >: 8
{ $0.someProperty < $1.someProperty }: 19
{ $0.someProperty > $1.someProperty }: 6

.sort {
total: 8
block with <: 3
block with >: 2
{ $0.someProperty < $1.someProperty }: 3
{ $0.someProperty > $1.someProperty }: 2

.sort(by: {
total: 1
block with <: 1
block with >: 0
{ $0.someProperty < $1.someProperty }: 1
{ $0.someProperty > $1.someProperty }: 0

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