FailableCodableArray Property wrapper

FailableCodableArray.swift

import Foundation

@propertyWrapper
struct FailableCodableArray<Element: Codable>: Codable {
    private struct AnyDecodableValue: Codable {}
    
    private struct FailableDecodableValue<Value: Codable>: Codable {
        let value: Value
        
        public init(from decoder: Decoder) throws {
            let container = try decoder.singleValueContainer()
            value = try container.decode(Value.self)
        }
    }
    
    var wrappedValue: [Element]
    
    init(wrappedValue: [Element]) {
        self.wrappedValue = wrappedValue
    }
    
    init(from decoder: Decoder) throws {
        var container = try decoder.unkeyedContainer()
        
        var elements: [Element] = []
        
        while !container.isAtEnd {
            do {
                let value = try container.decode(FailableDecodableValue<Element>.self).value
                elements.append(value)
            } catch {
                /* Without writing this it turns into infinite loop due to the 
                 implementation of UnkeyedDecodingContainer.currentIndex. 
                Because the currentIndex is not incremented unless a decode succeeds. */
                _ = try? container.decode(AnyDecodableValue.self)
                continue
            }
        }
        self.wrappedValue = elements
    }
    
    func encode(to encoder: Encoder) throws {
        try wrappedValue.encode(to: encoder)
    }
}

struct Response: Codable {
    @FailableCodableArray var favorites: [Favorite]
}

enum Favorite: String, Codable {
    case falcon
    case penguin
}

let json = #"{ "favorites": ["falcon", "penguin", "peacock"] }"#.data(using: .utf8)!
let result = try JSONDecoder().decode(Response.self, from: json)

print(result)