using System;

​

public struct MyDateOnly

{

    private readonly int _dayNumber;

    public MyDateOnly(int year, int month, int day) => _dayNumber = year;

}

internal class Program

{

    static void Main(string[] args)

    {

        TryParse("abc", out MyDateOnly d);

    }

​

    public static void TryParse(string s, out MyDateOnly dateOnly) { }

}