Program.cs

using System.Runtime.CompilerServices;

namespace WeakRefs;

internal class Program
{
    private static WeakCache<string, byte[]> cache = new();
    private static byte[]? data = new byte[100];

    private static void Main(string[] args)
    {
        AddData();
        CheckStillAvailable();

        GC.Collect();
        CheckStillAvailable();

        SetOnlyRootToNull();
        GC.Collect();
        CheckNoLongerAvailable();
    }

    [MethodImpl(MethodImplOptions.NoInlining)]
    private static void AddData()
    {
        cache.Add("d", data!);
    }

    [MethodImpl(MethodImplOptions.NoInlining)]
    private static void CheckStillAvailable()
    {
        Console.WriteLine("Retrieval: " +
            cache.TryGetValue("d", out byte[]? fromCache));
        Console.WriteLine("Same ref?  " +
            object.ReferenceEquals(data, fromCache));
    }

    [MethodImpl(MethodImplOptions.NoInlining)]
    private static void SetOnlyRootToNull()
    {
        data = null;
    }

    [MethodImpl(MethodImplOptions.NoInlining)]
    private static void CheckNoLongerAvailable()
    {
        byte[]? fromCache;
        Console.WriteLine("Retrieval: " + cache.TryGetValue("d", out fromCache));
        Console.WriteLine("Null?  " + (fromCache == null));
    }
}