プライマリ関連型と型付きthrows

protocol Container<Element> {
  associatedtype Element
  var items: [Element] { get }
}
struct Bag<T>: Container { var items: [T] = [] }

func printItems(_ c: any Container<Int>) {
  c.items.forEach { print($0) }
}
printItems(Bag(items: [1,2,3]))

func first(_ c: any Collection<String>) -> String? {
  c.first
}
print(first(["a","b","c"]) ?? "none")

enum NetworkError: Error { case timeout, notFound }
func fetch() throws(NetworkError) -> Data {
  throw NetworkError.timeout
}

do {
  let _ = try fetch()
} catch .timeout {
  print("Timed out")
} catch .notFound {
  print("Not found")
}

protocol Fetchable {
  associatedtype Failure: Error
  func fetch() throws(Failure) -> Data
}

func map<T, E: Error>(_ array: [T], transform: (T) throws(E) -> T) throws(E) -> [T] {
  try array.map { try transform($0) }
}

protocol Repository<Model> {
  associatedtype Model
  associatedtype Failure: Error
  func fetchAll() throws(Failure) -> [Model]
}

func riskyOp() throws(any Error) {
  // can throw any error
}

// Before:
func load() throws -> Data { ... }
// After:
func load() throws(NetworkError) -> Data { ... }

func fetchAsync() async throws(NetworkError) -> Data {
  throw NetworkError.notFound
}