namespace System.Collections.Immutable
{
    [DefaultMember("Item")]
    public sealed class ImmutableDictionary<TKey, TValue> : ICollection<KeyValuePair<TKey, TValue>>, IDictionary<TKey, TValue>, IEnumerable, IEnumerable<KeyValuePair<TKey, TValue>>, IReadOnlyCollection<KeyValuePair<TKey, TValue>>, IReadOnlyDictionary<TKey, TValue>, ICollection, IDictionary, IImmutableDictionary<TKey, TValue>
        where TKey, notnull
    {
        public TValue this[TKey key] { get; }
    }
}