Query.cs

public readonly unsafe struct Query : IEnumerable<Iterator>
{
    private readonly World _world = null!;
	private readonly ecs_query_t* _handle = null;

	public Query(World world, string expr)
	{
		ecs_query_desc_t desc = default;
		desc.filter.expr = expr;
		_world  = world;
		_handle = ecs_query_init(world.Handle, &desc);
	}

	public void Fini()
		=> ecs_query_fini(_handle);

	public IEnumerator<Iterator> GetEnumerator() => new QueryIterator(this);
	IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();

	private struct QueryIterator : IEnumerator<Iterator>
	{
		private readonly ecs_iter_t _iter;

		public QueryIterator(Query query)
			=> _iter = ecs_query_iter(query._world.Handle, query._handle);

		public bool MoveNext()
		{
			fixed (QueryIterator* @this = &this)
				return ecs_query_next(&@this->_iter);
		}

		object IEnumerator.Current => Current;
		public Iterator Current { get {
			fixed (QueryIterator* @this = &this)
				return new(World.Pointers[(IntPtr)@this->_iter.world], &@this->_iter);
		} }

		public void Reset() => throw new NotSupportedException();
		public void Dispose() {  }
	}
}