Data container which express single or multiple ojects

SingleOrMultiple.swift

enum SingleOrMultiple<Value> {
    case single(Value)
    case multiple([Value])
    
    func map<T>(_ transform: (Value) throws -> T) rethrows -> SingleOrMultiple<T> {
        switch self {
        case let .single(value): return .single(try transform(value))
        case let .multiple(values): return .multiple(try values.map(transform))
        }
    }
    
    func flatMap<T>(_ transform: (Value) throws -> SingleOrMultiple<T>) rethrows -> SingleOrMultiple<T> {
        switch self {
        case let .single(value):
            return try transform(value)
        case let .multiple(values):
            return .multiple(try values // [Value]
                .map(transform) // [SingleOrMultiple<T>]
                .flatMap { $0.array } // [T]
            )
        }
    }
    
    var array: [Value] {
        switch self {
        case let .single(value): return [value]
        case let .multiple(values): return values
        }
    }
    
    var first: Value? {
        return array.first
    }
    
}