last.swift

extension Sequence {
  func last(where predicate: (Element) throws -> Bool) rethrows -> Element? {
    var result: Element? = nil
    for el in self {
      if try predicate(el) {
        result = el
      }
    }
    return result
  }
}

extension Collection {
  func lastIndex(where predicate: (Element) throws -> Bool) rethrows -> Index? {
    var result: Index? = nil
    var i = startIndex
    while i < endIndex {
      if try predicate(self[i]) {
        result = i
      }
      formIndex(after: &i)
    }
    return result
  }
}

extension Collection where Element: Equatable {
  func lastIndex(of element: Element) -> Index? {
    return lastIndex(where: { $0 == element })
  }
}

extension BidirectionalCollection {
  func last(where predicate: (Element) throws -> Bool) rethrows -> Element? {
    var i = endIndex
    while i > startIndex {
      formIndex(before: &i)
      if try predicate(self[i]) {
        return self[i]
      }
    }
    return nil
  }
  
  func lastIndex(where predicate: (Element) throws -> Bool) rethrows -> Index? {
    return try indices.last(where: { try predicate(self[$0]) })
  }
}

extension BidirectionalCollection where Element: Equatable {
  func lastIndex(of element: Element) -> Index? {
    return lastIndex(where: { $0 == element })
  }
}

let a = [20, 30, 10, 40, 20, 30, 10, 40, 20]
a.last(where: { $0 > 25 })          // 40
a.lastIndex(where: { $0 > 25 })     // 7
a.lastIndex(of: 10)                 // 6