ResultPattern.cs

public class Result<T>
{
    public T Value { get; }
    public string Error { get; }
    public bool IsSuccess => Error == null;

    private Result(T value, string error)
    {
        Value = value;
        Error = error;
    }

    public static Result<T> Success(T value) => new(value, null);
    public static Result<T> Failure(string error) => new(default, error);
}


[ApiController]
[Route("api/users")]
public class UserController : ControllerBase
{
    private static readonly Dictionary<int, string> Users = new()
    {
        { 1, "Alice" },
        { 2, "Bob" }
    };

    [HttpGet("{id}")]
    public ActionResult<Result<string>> GetUser(int id)
    {
        var result = GetUserById(id);
        if (!result.IsSuccess)
        {
            return BadRequest(result);
        }
        return Ok(result);
    }

    private Result<string> GetUserById(int id)
    {
        if (Users.TryGetValue(id, out var user))
        {
            return Result<string>.Success(user);
        }
        return Result<string>.Failure("User not found.");
    }
}