System.Collections.Immutable.ImmutableHashSet
public static ImmutableHashSet<T> CreateRange<T>(IEqualityComparer<T> equalityComparer, IEnumerable<T> items)
public static ImmutableHashSet<TSource> ToImmutableHashSet<TSource>(this IEnumerable<TSource> source, IEqualityComparer<TSource> equalityComparer)
public static ImmutableHashSet<TSource> ToImmutableHashSet<TSource>(this IEnumerable<TSource> source)