// PROJECT-EXAMPLE
int Double(in int value) => value * 2;
int count = 3;
System.Console.WriteLine(Double(in count));

Method(in value) / interface IConsumer<in T> / foreach (var x in items)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.IO;
using System.Runtime.InteropServices;
using System.Runtime.CompilerServices;

public static class Program
{
    public static async Task Main(string[] args)
    {
        Point value = new(2, 3);
        Console.WriteLine(Geometry.Sum(in value));
    }
}
public readonly record struct Point(int X, int Y);
public static class Geometry { public static int Sum(in Point value) => value.X + value.Y; }

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.IO;
using System.Runtime.InteropServices;
using System.Runtime.CompilerServices;

public static class Program
{
    public static async Task Main(string[] args)
    {
        IConsumer<object> broad = new Writer();
        IConsumer<string> narrow = broad;
        narrow.Accept("ore");
    }
}
public interface IConsumer<in T> { void Accept(T value); }
public class Writer : IConsumer<object> { public void Accept(object value) { Console.WriteLine(value); } }