using System;

using System.Diagnostics.CodeAnalysis;

​

namespace ConsoleApp3

{

#nullable enable

    class Program

    {

        static void Main(string[] args)

        {

            IResult<string> res = GetSomeResult();

            if (!res.IsSuccess())

                throw new Exception(); // or just return something else

​

            var len = res.Data.Length; // no nullability warning

        }

​

        static Result<string> GetSomeResult()

        {

            return new Result<string>(string.Empty);

        }

    }

​

    public interface IResult<out T>

    {

        [MemberNotNullWhen(true, nameof(Data))]

        bool IsSuccess();

        T? Data { get; }

    }

​

    public class Result<T> : IResult<T>

    {

        private readonly T? _data;

        public T? Data => _data;

​

        public Result(T? data)

        {

            _data = data;

        }

​

        public bool IsSuccess() => _data != null;

    }

}

​