func OptIndexKeys(keys bool) IndexOption {
	return func(options *IndexOptions) {
		options.keys = keys
		options.keysSet = true
	}
}
func OptIndexKeys(keys bool) IndexOption {
	return func(options *IndexOptions) {
		options.keys = keys
		options.keysSet = true
	}
}
// OptIndexKeys sets whether index uses string keys.