ArrayOrValue.swift

public enum ArrayOrValue<Value>: Codable
where Value: Codable {

    case array([Value])
    case value(Value)

    public init(from decoder: Decoder) throws {
        do {
            let container = try decoder.singleValueContainer()
            self = .value(try container.decode(Value.self))
        }
        catch {
            var container = try decoder.unkeyedContainer()
            var array: [Value]
            if container.count != nil {
                array = []
                while !container.isAtEnd {
                    array.append(try container.decode(Value.self))
                }
            }
            else {
                // NOTE: Trick to raise lazy-crashing
                array = unsafeBitCast(Optional<[Value]>(nilLiteral: ()), to: [Value].self)
            }
            self = .array(array)
        }
    }

    public func encode(to encoder: Encoder) throws {
        switch self {
        case .array(let array):
            var container = encoder.unkeyedContainer()
            try container.encode(contentsOf: array)
        case .value(let value):
            var container = encoder.singleValueContainer()
            try container.encode(value)
        }
    }
}