// in MyLibrary.swift =======
@freestanding(expression)
macro MyFileID<T: ExpressibleByStringLiteral>() -> T = ...

public func callSiteFile(_ file: String = #MyFileID) { file }

public func declarationSiteFile(_ file: String = (#MyFileID)) { file }

public func alsoDeclarationSiteFile(
    file: String = callSiteFile(#MyFileID)
) { file }

// in main.swift ============
print(callSiteFile())            // print main.swift, the current file
print(declarationSiteFile())     // always prints MyLibrary.swift
print(alsoDeclarationSiteFile()) // always prints MyLibrary.swift

@available(SwiftStdlib 5.1, *)
protocol AsyncIteratorProtocol<Element, Failure> {
  associatedtype Element

  mutating func next() async throws -> Element?

  @available(SwiftStdlib 6.0, *)
  associatedtype Failure: Error = any Error

  @available(SwiftStdlib 6.0, *)
  mutating func next(isolation actor: isolated (any Actor)?) async throws(Failure) -> Element?
}

@available(SwiftStdlib 5.1, *)
public protocol AsyncSequence<Element, Failure> {
  associatedtype AsyncIterator: AsyncIteratorProtocol
  associatedtype Element where AsyncIterator.Element == Element

  @available(SwiftStdlib 6.0, *)
  associatedtype Failure = AsyncIterator.Failure where AsyncIterator.Failure == Failure

  func makeAsyncIterator() -> AsyncIterator
}

extension AsyncIteratorProtocol {
  func next(isolation: isolated (any Actor)? = #isolation) async -> Element {
    ...
  }
}

// You write this:
let f: (User) -> String? = \User.email

// The compiler generates something like this:
let f: (User) -> String? = { kp in { root in root[keyPath: kp] } }(\User.email)

func iterate<each Element>(over element: repeat each Element) {
  for element in repeat each element {
  
  }
}

extension String {
  public init?<Encoding: Unicode.Encoding>(
    validating codeUnits: some Sequence<Encoding.CodeUnit>,
    as: Encoding.Type
  )
}

var numbers = Array(1...15)

// Find the indices of all the even numbers
let indicesOfEvens = numbers.indices(where: { $0.isMultiple(of: 2) })

// Perform an operation with just the even numbers
let sumOfEvens = numbers[indicesOfEvens].reduce(0, +)
// sumOfEvens == 56

// You can gather the even numbers at the beginning
let rangeOfEvens = numbers.moveSubranges(indicesOfEvens, to: numbers.startIndex)
// numbers == [2, 4, 6, 8, 10, 12, 14, 1, 3, 5, 7, 9, 11, 13, 15]
// numbers[rangeOfEvens] == [2, 4, 6, 8, 10, 12, 14]