gistfile1.cs

public interface IResult<T> {
   bool Success { get; }
   T Data { get; }
   string Error { get; }
}

public class ErrorResult<T> : Result<T> {
	
	public ErrorResult(string error) : base(null, false, error) {
		
	}
}

public class SuccessResult<T> : Result<T> {
	public SuccessResult(T data) : base(data, true, "") {
		
	}
}

public class Result<T> : IResult<T> {
	
	public bool Success {get; private set;}
	public T Data {get; private set;}
	public string Error {get; private set; }
	
	public Result(T data, bool success, string error) {
		Data = data;
		Success = success;
		Error = error;
	}
	
	public static IResult<T> Success(T data) {
		return new Result(data, true, ""); // ELLER return new SuccessResult(data);
	}
	
	public static IResult<T> Error(string error) {
		return new Result(null, false, error); // ELLER return new ErrorResult(error);
	}
}

public IResult<T> Execute() {
   Query.Send(Param);    
   if (Query.Success) {
	return new SuccessResult(Query.Data);	
   } else {
   	return new ErrorResult(Query.Message);
   }
}

public IResult<T> Execute() {
   Query.Send(Param);
   if (Query.Success) {
	 return Result.Success(Query.Data);
   } else {
   	 return Result.Error(Query.Message);
   }
}