[swift-evolution] sortBy, minElementBy and maxElementBy methods

[Susan Cheng]

It's a choice with overriding methods or provide a global function which's
missing @noescape version and has to write documentation to telling people
what's it doing.

However, sortBy method is common in other languages.

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

> You don’t.  Is that a problem for the intended use-cases?
>
> -Dave
>
> On Dec 31, 2015, at 12:11 AM, Susan Cheng <susan.doggie at gmail.com
> <javascript:_e(%7B%7D,'cvml','susan.doggie at gmail.com');>> wrote:
>
> And how do you write a @noescape version with this function?
>
> Dave Abrahams <dabrahams at apple.com
> <javascript:_e(%7B%7D,'cvml','dabrahams at apple.com');>> 於 2015年12月31日星期四
> 寫道：
>
>> I don’t understand that argument.  Obviously the function would be
>> documented and there would be examples showing how to use it.  Why would it
>> confuse people?
>>
>> I think you’d need much stronger reasons to justify adding an unbounded
>> set of overloads (is every algorithm that takes a comparison closure going
>> to get one of these?) when we can handle the problem economically with a
>> single function.
>>
>> -Dave
>>
>> On Dec 31, 2015, at 12:04 AM, Susan Cheng <susan.doggie at gmail.com> wrote:
>>
>> 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> 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
>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>
>>>
>>>
>>
>
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