Controlling Type conversion in C#

Yan Cui

I help clients go faster for less using serverless technologies.

Ever run into a situation where your application needs to use a type for its internal working but occasionally need to convert that type into another just so it can be passed to another application which doesn’t understand some of the base types we have in the .Net space?

Consider the example below, where the Player is a type in my problem domain, but I need to communicate information about the player with a non-.Net client which doesn’t have the Guid type, so I need to have a PlayerDTO type used exclusively for message passing:

public sealed class Player
{
    public Player(string name, long score)
    {
        Name = name;
        Score = score;
        ID = Guid.NewGuid();
    }

    public string Name { get; private set; }
    public Guid ID { get; private set; }
    public long Score { get; private set; }
}

public sealed class PlayerDTO
{
    public PlayerDTO(string name, long score, string id)
    {
        Name = name;
        Score = score;
        ID = id;
    }

    public string Name { get; private set; }
    public string ID { get; private set; } // client is not .Net based so no Guid there
    public long Score { get; private set; }
}

The problem here is that there is no easy way to convert the Player type to PlayerDTO and every time I want to create a new PlayerDTO object I need to manually copy the values from Player into PlayerDTO’s constructor, and my application needs to know that it needs to convert Player.PlayerID into a string.

A cleaner solution here is to overload either the implicit or explicit converter so you can simply cast a Player object into a PlayerDTO object:

// Overload explicit cast converter to allow easy conversion from a Winner to WinnerAmfvo object
public static explicit operator PlayerDTO(Player player)
{
    return new PlayerDTO(player.Name, player.Score, player.PlayerID.ToString());
}

Further more, this allows you to easily convert an array of Player objects into an array of PlayerDTO objects:

// use Array.ConvertAll
PlayerDTO[] playerDTOs = Array.ConvertAll(players, p => (PlayerDTO) p);
// use Linq
playerDTOs = players.Select(p => (PlayerDTO) p).ToArray();

playerDTOs = iPlayers.Select(p => PlayerDTO.FromPlayer(p)).ToArray();

playerDTOs = iPlayers.Select(p => PlayerConvert.ToPlayerDTO(p)).ToArray();

StackOverflow question on why you can't use interface types with implicit/explicit operator