begin work on reflection-based scanner

Signed-off-by: oppiliappan <[e-mail]>

scanner.go

···
+package norm
+
+import (
+	"database/sql"
+	"iter"
+	"reflect"
+)
+
+type Scanner[T any] struct {
+	rows    *sql.Rows
+	onError func(err error)
+}
+
+type ScannerOpt[T any] func(*Scanner[T])
+
+func OnScannerError[T any](errFunc func(error)) ScannerOpt[T] {
+	return func(s *Scanner[T]) {
+		s.onError = errFunc
+	}
+}
+
+func NewScanner[T any](rows *sql.Rows, opts ...ScannerOpt[T]) Scanner[T] {
+	scanner := Scanner[T]{
+		rows: rows,
+	}
+
+	for _, o := range opts {
+		o(&scanner)
+	}
+
+	return scanner
+}
+
+func (s *Scanner[T]) Scan() iter.Seq[T] {
+	return func(yield func(T) bool) {
+		defer s.rows.Close()
+
+		for s.rows.Next() {
+			var data T
+			elem := reflect.ValueOf(&data).Elem()
+			numCols := elem.NumField()
+			columns := make([]any, numCols)
+
+			for i := range numCols {
+				field := elem.Field(i)
+				columns[i] = field.Addr().Interface()
+			}
+
+			if err := s.rows.Scan(columns...); err != nil {
+				s.onError(err)
+				return
+			}
+
+			// Yield the row - if yield returns false, stop iteration
+			if !yield(data) {
+				return
+			}
+		}
+	}
+}