// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
 
using System.Collections.Generic;
 
namespace Roslyn.Utilities;
 
/// <summary>
/// A simple collection of values held as weak references. Objects in the set are compared by reference equality.
/// </summary>
/// <typeparam name="T">The type of object stored in the set.</typeparam>
internal sealed class WeakSet<T>
    where T : class?
{
    private readonly HashSet<ReferenceHolder<T>> _values = [];
 
    public WeakSet()
    {
    }
 
    public bool Add(T value)
    {
        if (Contains(value))
            return false;
 
        return _values.Add(ReferenceHolder<T>.Weak(value));
    }
 
    public bool Contains(T value)
    {
        return _values.Contains(ReferenceHolder<T>.Strong(value));
    }
}