Add support for Promise races

Sources/Pwomise/Pwomise.swift

@@ -7,12 +7,36 @@ public protocol PromiseConvertible {
  var asPromise: Promise<Output> { get }
 }
 
+public enum PromiseInconsistencyError: Error {
+ case emptyArray
+}
+
 public class Promise<Output>: CustomDebugStringConvertible {
  internal typealias Pending = PendingPromise<Output, Error>
  public typealias Completion = Result<Output, Error>
  public typealias Resolve = (Output) -> ()
  public typealias Reject = (Error) -> ()
 
+ public static func any(_ promises: [Promise<Output>]) -> Promise<Output> {
+ guard promises.count > 0 else {
+ return .failure(PromiseInconsistencyError.emptyArray)
+ }
+
+ let superPromise = Promise()
+
+ for promise in promises {
+ promise.always { completion in
+ guard superPromise.pending else {
+ return
+ }
+
+ superPromise.result = .resolved(completion)
+ }
+ }
+
+ return superPromise
+ }
+
  public static func all(_ promises: [Promise<Output>]) -> Promise<[Output]> {
  guard promises.count > 0 else {
  return .success([])

Tests/PwomiseTests/PwomiseTests.swift

@@ -2,5 +2,20 @@
  @testable import Pwomise
 
  final class PwomiseTests: XCTestCase {
-
+ func testRace() {
+ var fulfilled = false
+
+ Promise<Void>.any([
+ Promise { resolve, reject in
+ resolve(())
+ },
+ Promise { resolve, reject in
+ resolve(())
+ }
+ ]).then { _ in
+ XCTAssert(!fulfilled, "resolved multiple times")
+
+ fulfilled = true
+ }
+ }
  }