Implement a struct-to-csv writer in Go - go

Question

The following code attempt to implement a generic CSV writer for any simple struct. By "simple", I mean field value of the struct are of standard, simple types (int, string etc).
type (
CSV interface {
Header() []string
String([]string) (string, error)
}
CSVArray []CSV
)
func CSVOutput(w io.Writer, data CSVArray, cols []string) error {
if len(data) == 0 {
return nil
}
_, err := fmt.Fprintln(w, data[0].Header())
if err != nil {
return err
}
for _, d := range data {
str, err := d.String(cols)
if err != nil {
return err
}
_, err = fmt.Fprintln(w, str)
if err != nil {
return err
}
}
return nil
}
The problem is CSVOutput() does not actually work. e.g.:
var data []Employee //the Employee struct implements CSV interface
CSVOutput(w, data, nil)
Compilation failed: cannot use data (type []Employee) as type CSVArray in argument to CSVOutput
I understand that []CSV is not same as []Employee, as explained here, and many other resources available online.
That said, is it possible to rewrite the CSVOutput() function by using reflection:
func CSVOutput(w io.Writer, data interfac{}, cols []string) error {
sliceOfIntf = castToSlice(data) //how to do this?
if !implementedCSV(sliceOfIntf[0]) { //and how to do this?
return errors.New("not csv")
}
... ...
}

Answer 1

is it possible to rewrite the CSVOutput() function by using reflection
Yes
// if data is []Employee{...}, then you can do the following:
rv := reflect.ValueOf(data)
if rv.Kind() != reflect.Slice {
return fmt.Errorf("data is not slice")
}
if !rv.Type().Elem().Implements(reflect.TypeOf((*CSV)(nil)).Elem()) {
return fmt.Errorf("slice element does not implement CSV")
}
csvArr := make(CSVArray, rv.Len())
for i := 0; i < rv.Len(); i++ {
csvArr[i] = rv.Index(i).Interface().(CSV)
}
// now csvArr is CSVArray containing all the elements of data
https://go.dev/play/p/gcSOid533gx