New C# features

gistfile1.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Console;

namespace RoslynTests
{
    class Program
    {
        static void Main(string[] args)
        {
            var chris = new Person("Chris", "20");
            chris.Details = new Dictionary<string, string>() {["job"] = "software engineer" };

            WriteLine(chris.SayHi());
        }
    }

    public class Person(string name, string age)
    {
        public string Name { get; } = name;
        private string _age = age;

        public Dictionary<string, string> Details { get; set; } = null;


        public string SayHi()
        {
            var greeting = new StringBuilder();
            greeting.AppendFormat("Hello {0}, ", Name);
            if (int.TryParse(_age, out int a))
                greeting.AppendFormat("I see you are {0} years old.", _age);

            if (Details != null && Details.Count > 0)
            {
                greeting.AppendLine();
                greeting.AppendLine("DETAILS:");
                foreach (var detail in Details)
                    greeting.AppendLine(string.Format("{0} = {1}", detail.Key, detail.Value));
            }
            return greeting.ToString();
        }
    }
}