I guess I didn't ask an actual question... is there a more idiomatic way of
doing this?
Thank you!
-- Salvatore
smile.
On Monday, July 24, 2023 at 4:00:59 PM UTC-4 Salvatore Domenick Desiano
wrote:
> Ever since 1.18 came out I've been struggling to find an idiomatic way to
> implement a certain kind of adapter. I'm starting to suspect I'm Holding It
> Wrong (TM) so here I am.
>
> In short, I have an adapter that is effectively a collection of static
> methods and it doesn't look right.
>
> Imagine you have a generic key-value database (transaction and life-cycle
> methods omitted for brevity):
>
> type SimpleDatabase interface {
> Get(t ViewTransaction, key string) ([]byte, bool, error)
> Put(t UpdateTransaction, key string, value []byte) error
> }
>
> You then want to build something more specific on top using generics to
> avoid repetition of tricky code:
>
> type ApplicationDatabase struct {
> impl *SimpleDatabase
> }
>
> func (db *ApplicationDatabase) PutProjectRecord(t UpdateTransaction, r
> *ProjectRecord) error {
> return put[ProjectRecord](db.impl, projectRecordFactory, t, r)
> }
>
> type recordFactory[V any] interface {
> dbKey(value V) string
> encodeValue(value V) []byte
> decodeValue(data []byte) (V, error)
> }
>
> func put[V any](db *SimpleDatabase, f *recordFactory[V], t
> UpdateTransaction, value V) error {
> key := f.dbKey(value)
> valueBytes := f.encodeValue(value)
> if err := db.put(t, key, valueBytes); err != nil
> return fmt.Errorf("db error: %w", err)
> }
> return nil
> }
>
> This is nice and clean -- adding a new record type is just a matter of
> adding a new recordFactory implementation. Adding more complexity to the
> put/get (recovery, etc.) only has to happen once. The part that bugs me,
> though, is that the implementation has no state and really looks like it
> shouldn't be instantiated:
>
> type projectRecordFactory struct{}
> func (f *projectRecordFactory) dbKey() string { return .... }
> func (f *projectRecordFactory) encodeValue(value V) []byte {
> json.Marshal(...) }
> func (f *projectRecordFactory) decodeValue(data []byte) (V, error) {
> json.Unmarshal(...) }
>
> and, frankly, if I didn't instantiate it, it would feel like either Java
> or C++ metaprogramming.
>
> I'm open to a completely different structure but I am really hoping to add
> new record types by adding a new package or type.
>
> Thanks!
>
> -- Salvatore
> smile.
>
>
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