TruthyValue.swift

import Foundation

struct TruthyValue {
    var value: Bool?
    init(_ value: Bool?) {
        self.value = value
    }
    
    init(_ value: Int) {
        switch value {
        case 0:
            self.init(false)
        case 1:
            self.init(true)
        default:
            self.init(nil)
        }
    }
    
    init(_ value: String) {
        switch value.lowercased() {
        case "false", "f", "no", "n", "0":
            self.init(false)
        case "true", "t", "yes", "y", "1":
            self.init(true)
        default:
            self.init(nil)
        }
    }
}


extension TruthyValue: Decodable {
    enum DecodingError: Error {
        case invalidType
    }
    
    init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()
        if let booleanValue = try? container.decode(Bool.self) {
            self.init(booleanValue)
        } else if let integerValue = try? container.decode(Int.self) {
            self.init(integerValue)
        } else if let stringValue = try? container.decode(String.self) {
            self.init(stringValue)
        } else {
            throw DecodingError.invalidType
        }
    }
}


let json = """
[true, "true", "t", "YES", "y", 1]
""".data(using: .utf8)!

let decoder = JSONDecoder()
let decoded = try decoder.decode([TruthyValue].self, from: json)
let arrayOfTruthValues = decoded.map { $0.value }
arrayOfTruthValues // [true, true, true, true, true, true]