Get list of active items from ConditionalWeakTable<T>

I ended up creating my own wrapper:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.CompilerServices;

public sealed class ConditionalHashSet<T> where T : class
{
    private readonly object locker = new object();
    private readonly List<WeakReference> weakList = new List<WeakReference>();
    private readonly ConditionalWeakTable<T, WeakReference> weakDictionary =
        new ConditionalWeakTable<T, WeakReference>();

    public void Add(T item)
    {
        lock (this.locker)
        {
            var reference = new WeakReference(item);
            this.weakDictionary.Add(item, reference);
            this.weakList.Add(reference);
            this.Shrink();
        }
    }

    public void Remove(T item)
    {
        lock (this.locker)
        {
            WeakReference reference;

            if (this.weakDictionary.TryGetValue(item, out reference))
            {
                reference.Target = null;
                this.weakDictionary.Remove(item);
            }
        }
    }

    public T[] ToArray()
    {
        lock (this.locker)
        {
            return (
                from weakReference in this.weakList
                let item = (T)weakReference.Target
                where item != null
                select item)
                .ToArray();
        }
    }

    private void Shrink()
    {
        // This method prevents the List<T> from growing indefinitely, but 
        // might also cause  a performance problem in some cases.
        if (this.weakList.Capacity == this.weakList.Count)
        {
            this.weakList.RemoveAll(weak => !weak.IsAlive);
        }
    }
}

In some recent framework version, the ConditionalWeakTable<TKey,TValue> now implements IEnumerator interface. Check out Microsoft Docs.

This applies to

• .NET Core >= 2.0
• .NET Standard >= 2.1

This is not solving the problem if someone is stuck with .NET Framework. Otherwise, this may help if, like me, it's only a matter of updating from .NET Standard 2.0 to 2.1.