From 88932f7e4c8545d4dc913080e2144cc24cd84942 Mon Sep 17 00:00:00 2001
From: Syo Ikeda <suicaicoca@gmail.com>
Date: Wed, 28 Dec 2016 01:29:40 +0900
Subject: [PATCH] Add `ResultProtocol.fanout(_:)` as an alternative to `&&&`
 operator

---
 Result/ResultProtocol.swift         | 10 +++++++-
 Tests/ResultTests/ResultTests.swift | 40 ++++++++++++++---------------
 2 files changed, 28 insertions(+), 22 deletions(-)

diff --git a/Result/ResultProtocol.swift b/Result/ResultProtocol.swift
index 634debf..88bd355 100644
--- a/Result/ResultProtocol.swift
+++ b/Result/ResultProtocol.swift
@@ -51,6 +51,14 @@ public extension ResultProtocol {
 			ifFailure: Result<U, Error>.failure)
 	}
 
+	/// Returns a Result with a tuple of the receiver and `other` values if both
+	/// are `Success`es, or re-wrapping the error of the earlier `Failure`.
+	public func fanout<R: ResultProtocol>(_ other: @autoclosure () -> R) -> Result<(Value, R.Value), Error>
+		where Error == R.Error
+	{
+		return self.flatMap { left in other().map { right in (left, right) } }
+	}
+
 	/// Returns a new Result by mapping `Failure`'s values using `transform`, or re-wrapping `Success`es’ values.
 	public func mapError<Error2>(_ transform: (Error) -> Error2) -> Result<Value, Error2> {
 		return flatMapError { .failure(transform($0)) }
@@ -119,7 +127,7 @@ infix operator &&& : LogicalConjunctionPrecedence
 public func &&& <L: ResultProtocol, R: ResultProtocol> (left: L, right: @autoclosure () -> R) -> Result<(L.Value, R.Value), L.Error>
 	where L.Error == R.Error
 {
-	return left.flatMap { left in right().map { right in (left, right) } }
+	return left.fanout(right)
 }
 
 precedencegroup ChainingPrecedence {
diff --git a/Tests/ResultTests/ResultTests.swift b/Tests/ResultTests/ResultTests.swift
index 072ab07..87a92fc 100644
--- a/Tests/ResultTests/ResultTests.swift
+++ b/Tests/ResultTests/ResultTests.swift
@@ -17,6 +17,24 @@ final class ResultTests: XCTestCase {
 		XCTAssert(Result(nil, failWith: error) == failure)
 	}
 
+	func testFanout() {
+		let resultSuccess = success.fanout(success)
+		if let (x, y) = resultSuccess.value {
+			XCTAssertTrue(x == "success" && y == "success")
+		} else {
+			XCTFail()
+		}
+
+		let resultFailureBoth = failure.fanout(failure2)
+		XCTAssert(resultFailureBoth.error == error)
+
+		let resultFailureLeft = failure.fanout(success)
+		XCTAssert(resultFailureLeft.error == error)
+
+		let resultFailureRight = success.fanout(failure2)
+		XCTAssert(resultFailureRight.error == error2)
+	}
+
 	func testBimapTransformsSuccesses() {
 		XCTAssertEqual(success.bimap(
 			success: { $0.characters.count },
@@ -168,26 +186,6 @@ final class ResultTests: XCTestCase {
 		let result = Result<String, AnyError>.success("fail").tryMap(tryIsSuccess)
 		XCTAssert(result == failure)
 	}
-
-	// MARK: Operators
-
-	func testConjunctionOperator() {
-		let resultSuccess = success &&& success
-		if let (x, y) = resultSuccess.value {
-			XCTAssertTrue(x == "success" && y == "success")
-		} else {
-			XCTFail()
-		}
-
-		let resultFailureBoth = failure &&& failure2
-		XCTAssert(resultFailureBoth.error == error)
-
-		let resultFailureLeft = failure &&& success
-		XCTAssert(resultFailureLeft.error == error)
-
-		let resultFailureRight = success &&& failure2
-		XCTAssert(resultFailureRight.error == error2)
-	}
 }
 
 final class NoErrorTests: XCTestCase {
@@ -269,6 +267,7 @@ extension ResultTests {
 			("testMapRewrapsFailures", testMapRewrapsFailures),
 			("testInitOptionalSuccess", testInitOptionalSuccess),
 			("testInitOptionalFailure", testInitOptionalFailure),
+			("testFanout", testFanout),
 			("testErrorsIncludeTheSourceFile", testErrorsIncludeTheSourceFile),
 			("testErrorsIncludeTheSourceLine", testErrorsIncludeTheSourceLine),
 			("testErrorsIncludeTheCallingFunction", testErrorsIncludeTheCallingFunction),
@@ -289,7 +288,6 @@ extension ResultTests {
 //			("testTryProducesSuccessesForOptionalAPI", testTryProducesSuccessesForOptionalAPI),
 			("testTryMapProducesSuccess", testTryMapProducesSuccess),
 			("testTryMapProducesFailure", testTryMapProducesFailure),
-			("testConjunctionOperator", testConjunctionOperator),
 		]
 	}
 }