Why not remove the `recordFactory` type then?
type Record interface {
Key() string
Marshal() []byte
Unmarshal([]byte) error
}
func put[R Record](db *SimpleDatabase, t UpdateTransaction, v R) error {
k := v.Key()
b := v.Marshal()
if err := db.put(t, k, b); err != nil {
return fmt.Errorf("db error: %w", err)
}
return nil
}
You might need to do the Pointer Receiver Trick (not sure if there's an FAQ
entry to link to here, so I'll just link to my not super great talk
<https://youtu.be/QP6v-Q5Foek?t=2718> explaining it) to implement get, i.e.:
type Record[T any] interface {
*T
Key() string
Marshal() []byte
Unmarshal([]byte) error
}
func get[R any, PR[R]](db *SimpleDatabase, t ViewTransaction) (R, error) {
var r R
k := PR(&r).Key()
b, err := db.get(t, k)
if err != nil {
return r, err
}
err = PR(&r).Unmarshal(b)
return r, err
}
(Note: This assumes that the `Key() string` method is still stateless, but
ISTM your factory type assumes that as well?)
On Fri, Jul 28, 2023 at 10:48 AM Salvatore Domenick Desiano <
neard...@gmail.com> wrote:
> 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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