using System;

using ValueOf;

using Dawn;

public class Program

{

    public static void Main()

    {

        PostingId? mome = GetPostingId();

        Console.WriteLine(mome);

    }

    public static PostingId? GetPostingId(){

        return (PostingId?)null;

    }

}

​

public sealed class PostingId : ValueOf<long, PostingId>

{

    protected override void Validate()

    {

        Guard.Argument(Value, nameof(Value))

            .Positive(_ => "Идентификатор отправления должен быть больше 0");

    }

​

    public static implicit operator long(PostingId c) => c.Value;

​

    public static implicit operator PostingId(long v) => From(v);

}