selecsort.swift

extension MutableCollection where
  SubSequence: MutableCollection,
  SubSequence.Iterator.Element == Iterator.Element,
  SubSequence.SubSequence == SubSequence,
  Indices.Iterator.Element == Index,
  SubSequence.Indices.Iterator.Element == SubSequence.Index,
  Iterator.Element: Comparable {
    
    mutating func selectionSort() {
      if let minInd = indices.min(isOrderedBefore: { (i,j) in self[i] < self[j] }) {
        if minInd != startIndex { swap(&self[startIndex],&self[minInd]) }
        self[index(after: startIndex)..<endIndex].selectionSort()
      }
    }
    
    func selectionSorted() -> Self {
      var copy = self
      copy.selectionSort()
      return copy
    }
}

selecsortgen.swift

extension MutableCollection where
  SubSequence: MutableCollection,
  SubSequence.Iterator.Element == Iterator.Element,
  SubSequence.SubSequence == SubSequence,
  Indices.Iterator.Element == Index,
  SubSequence.Indices.Iterator.Element == SubSequence.Index {
    
    mutating func selectionSort(isOrderedBefore cmp: (Iterator.Element, Iterator.Element) -> Bool) {
      if let minInd = indices.min(isOrderedBefore: { (i,j) in cmp(self[i],self[j]) }) {
        if minInd != startIndex { swap(&self[startIndex],&self[minInd]) }
        self[index(after: startIndex)..<endIndex]
            .selectionSort(isOrderedBefore: cmp)
      }
    }
    
    func selectionSorted(isOrderedBefore cmp: (Iterator.Element, Iterator.Element) -> Bool) -> Self {
      var copy = self
      copy.selectionSort(isOrderedBefore: cmp)
      return copy
    }
}

extension MutableCollection where
  SubSequence: MutableCollection,
  SubSequence.Iterator.Element == Iterator.Element,
  SubSequence.SubSequence == SubSequence,
  Indices.Iterator.Element == Index,
  SubSequence.Indices.Iterator.Element == SubSequence.Index,
  Iterator.Element: Comparable {
    
    mutating func selectionSort() {
      selectionSort(isOrderedBefore: <)
    }
    
    func selectionSorted() -> Self {
      return selectionSorted(isOrderedBefore: <)
    }
}