Kingfisher/Sources/Utility/Result.swift

//
//  Result.swift
//  Kingfisher
//
//  Created by onevcat on 2018/09/22.
//
//  Copyright (c) 2018 Wei Wang <onevcat@gmail.com>
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in
//  all copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
//  THE SOFTWARE.

import Foundation

/// Represents a result of some operation, whether it is successful or an error happens.
///
/// - success: The operation is successful and an associated value could be provided.
/// - failure: An error happens during the operation.
public enum Result<Value> {
    case success(Value)
    case failure(Error)
    
    /// Returns `true` if the result is a success, `false` otherwise.
    public var isSuccess: Bool {
        if case .success = self {
            return true
        }
        return false
    }
    
    /// Returns the associated value if the result is a success, `nil` otherwise.
    public var value: Value? {
        if case .success(let v) = self {
            return v
        }
        return nil
    }
    
    /// Returns `true` if the result is a failure, `false` otherwise.
    public var failure: Bool {
        return !isSuccess
    }
    
    /// Returns the associated error value if the result is a failure, `nil` otherwise.
    public var error: Error? {
        if case .failure(let e) = self {
            return e
        }
        return nil
    }
    
    /// Map over the `Result` value. If it was a `.success`, `transform` closure will be applied to associated value
    /// and a new `.success` with transformed value will be returned. If it was a `.failure`, the same error will be
    /// returned.
    ///
    /// - Parameter transform: A closure that takes the success value of the instance.
    /// - Returns: A `Result` containing the result of the given closure. If this instance is a failure, returns the
    ///            same failure.
    public func map<T>(_ transform: (Value) -> T) -> Result<T> {
        switch self {
        case .success(let value): return .success(transform(value))
        case .failure(let error): return .failure(error)
        }
    }
}