func (f *filterBuilder) and(a *filterBuilder) {
	if f.subFilter != nil {
		f.setError(errSubFilterAlreadySet)
		return
	}

	f.subFilter = a
	f.subFilterOp = andOp
}
// and sets the sub-filter that will be ANDed with this one.
// Sets the error state if sub-filter is already set.
and sets the sub-filter that will be ANDed with this one.
Sets the error state if sub-filter is already set.
// and sets the sub - filter that will be ANDed with this one . // Sets the error state if sub - filter is already set .
func (f *filterBuilder) and(a *filterBuilder) {
	if f.subFilter != nil {
		f.setError(errSubFilterAlreadySet)
		return
	}
	f.subFilter = a
	f.subFilterOp = andOp
}
func ( f * filterBuilder ) and ( a * filterBuilder ) { if f . subFilter != nil { f . setError ( errSubFilterAlreadySet ) return } f . subFilter = a f . subFilterOp = andOp }
and sets the sub-filter that will be ANDed with this one.
and sets the sub - filter that will be ANDed with this one .