Graceful Decoding for Swift Decodable

Decodable+Graceful.swift

//
//  Decodable+Graceful.swift
//  Graceful Decodable
//
//  Created by Zack Sheppard on 9/10/20.
//  Copyright © 2020 Zack Sheppard. All rights reserved.
//  Available under the MIT License
//  Available at https://gist.github.com/zackdotcomputer/81b8545e3ce81128a299996814823963
//

import Foundation

// From https://medium.com/flawless-app-stories/how-to-safely-decode-arrays-using-decodable-result-type-in-swift-5b975ea11ff5
// A safe wrapper for rescuable decodable lists
public struct GracefulDecodable<T: Decodable>: Decodable {
    public let result: Result<T, Error>

    public init(from decoder: Decoder) throws {
        let catching = { try T(from: decoder) }
        result = Result(catching: catching )
    }
}

extension KeyedDecodingContainer {
    /// Try to decode a list of objects of a Decodable type, gracefully omitting those that fail to decode rather than failing the entire list.
    func decodeGracefulList<OfType: Decodable>(_ type: OfType.Type, forKey key: KeyedDecodingContainer<K>.Key) throws -> [OfType] {
        let values = try self.decode([GracefulDecodable<OfType>].self, forKey: key)
        return values.compactMap({ $0.result.value })
    }

    /// Try to decode a list of objects of a Decodable type if present, gracefully omitting those that fail to decode rather than failing the entire list.
    func decodeGracefulListIfPresent<OfType: Decodable>(_ type: OfType.Type, forKey key: KeyedDecodingContainer<K>.Key) throws -> [OfType]? {
        let values = try self.decodeIfPresent([GracefulDecodable<OfType>].self, forKey: key)
        return values?.compactMap({ $0.result.value })
    }
}