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