using System.Collections.Generic;

public static class HashSetExtensions
{
	public static void EnsureContains<T>(this HashSet<T> @this, T item, bool containsOrNot) where T : notnull
	{
		if (containsOrNot)
		{
			@this.Add(item);
		}
		else
		{
			@this.Remove(item);
		}
	}
}