namespace System.Collections.Concurrent
{
    [DefaultMember("Item")]
    public class ConcurrentDictionary<TKey, TValue> : ICollection<KeyValuePair<TKey, TValue>>, IDictionary<TKey, TValue>, IEnumerable, IEnumerable<KeyValuePair<TKey, TValue>>, IReadOnlyCollection<KeyValuePair<TKey, TValue>>, IReadOnlyDictionary<TKey, TValue>, ICollection, IDictionary
        where TKey, notnull
    {
        public TValue GetOrAdd<TArg>(TKey key, Func<TKey, TArg, TValue>! valueFactory, TArg factoryArgument);
    }
}