// 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;
using System.Collections.Generic;
 
namespace Roslyn.Utilities
{
    internal partial class SpecializedCollections
    {
        private partial class Empty
        {
            internal class Set<T> : Collection<T>, ISet<T>, IReadOnlySet<T>
            {
                public static new readonly Set<T> Instance = new();
 
                protected Set()
                {
                }
 
                public new bool Add(T item)
                {
                    throw new NotSupportedException();
                }
 
                public void ExceptWith(IEnumerable<T> other)
                {
                    throw new NotSupportedException();
                }
 
                public void IntersectWith(IEnumerable<T> other)
                {
                    throw new NotSupportedException();
                }
 
                public bool IsProperSubsetOf(IEnumerable<T> other)
                {
                    return !other.IsEmpty();
                }
 
                public bool IsProperSupersetOf(IEnumerable<T> other)
                {
                    return false;
                }
 
                public bool IsSubsetOf(IEnumerable<T> other)
                {
                    return true;
                }
 
                public bool IsSupersetOf(IEnumerable<T> other)
                {
                    return other.IsEmpty();
                }
 
                public bool Overlaps(IEnumerable<T> other)
                {
                    return false;
                }
 
                public bool SetEquals(IEnumerable<T> other)
                {
                    return other.IsEmpty();
                }
 
                public void SymmetricExceptWith(IEnumerable<T> other)
                {
                    throw new NotSupportedException();
                }
 
                public void UnionWith(IEnumerable<T> other)
                {
                    throw new NotSupportedException();
                }
            }
        }
    }
}