OperationResult is a Swift Package Manager package for iOS/tvOS (10.0 and above), watchOS (4.0 and above), and macOS (10.14 and above), under Swift 5.0 and above, defining an enumeration similar to Result but with Array<String> in place of an error type:
public enum OperationResult<A> {
case success(A)
case failure([String])
public var value: A?
public var failureMessages: [String]?
public var didSucceed: Bool
public var didFail: Bool
public func map<B> (_ transform: (A) -> B) -> OperationResult<B>
}
extension OperationResult: Equatable where A: Equatable {}
extension OperationResult: Hashable where A: Hashable {}
extension OperationResult: Codable where A: Codable {
enum CodingKeys: CodingKey {
case success
case failure
}
public func encode(to encoder: Encoder) throws
public init(from decoder: Decoder) throws
}One neat use for this type is when considering a long sequence of numerical operations, some of which may fail. For example, division by zero, logarithm of a non-positive number, arc-sine or arc-cosine of a number with a magnitude larger than 1, and so on. Rather than stop the execution with throw-catches or risk runtime errors, the OperationResult<A> type allows a clean progression to the end, accumulating error messages along the way. Here's a representative implementation, using division as an example:
typealias NumericalResult = OperationResult<Double>
extension NumericalResult {
static func / (lhs: NumericalResult, rhs: NumericalResult) -> NumericalResult {
switch (lhs, rhs) {
case let (.success(a), .success(b)):
guard b != 0 else { return .failure(["Division of \(a) by zero"]) }
return .success(a/b)
case let (.failure(a), .success(_)):
return .failure(a)
case let (.success(_), .failure(b)):
return .failure(b)
case let (.failure(a), .failure(b)):
return .failure(a + b)
}
}
}OperationResult is provided only as a Swift Package Manager package, because I'm moving away from CocoaPods and Carthage, and can be easily installed directly from Xcode.
OperationResult is available under the MIT license. See the LICENSE file for more info.