I see, thanks. It seems we have a couple options:
1. Add empty/0 to Collectable, but I have reservations since it is not a valid operation for all collectables 2. Another option is to introduce a :reset operation into the existing Collectable.into/2, but all in all it has the same issues as 1) 3. Introduce a new Empty protocol (potentially as a lib) 4. Ecto could introduce its own Ecto.Preloadable protocol. This would be beneficial if we can see other functionality being added around this. Are there other issues that returning Scrivener.Page introduces? 5. Perhaps there is a relationship between empty / traversal and the current Access module that could be leveraged too, but i can't see it right now. Perhaps Wiebe-Marten Wijnja can? *José Valim* www.plataformatec.com.br Skype: jv.ptec Founder and Director of R&D On Tue, May 21, 2019 at 7:30 PM Benjamin Milde <[email protected]> wrote: > It should basically „reset“ the part of the struct, which is used by the > Enumerable protocol implementation. > > def empty(page), do: %{page | elements: []} > > So that after an Enum.into(changes, SomeProtocol.empty(initial_page)) we > end up with exactly the same metadata, but different elements. > > On 21 May 2019, at 19:19, José Valim wrote: > > Thanks! And if we were to add a Collectable.empty, what would be its > implementation for Scrivener.Page? > > *José Valim* > www.plataformatec.com.br > Skype: jv.ptec > Founder and Director of R&D > > > On Tue, May 21, 2019 at 7:15 PM Benjamin Milde <[email protected]> > wrote: > >> Take for example https://github.com/drewolson/scrivener_ecto >> >> With a current version of ecto you can happily do this: >> >> ``` >> Repo.all(query) |> Repo.preload(:user) >> Repo.one(query) |> Repo.preload(:user) >> ``` >> >> but not this: >> >> ``` >> Repo.paginate(query) |> Repo.preload(:user) >> ``` >> >> Given that doing some work on results of db calls is quite common I tend >> to end up with lot's of functions pattern matching if results are >> `%Scrivener.Page{}`, a list or an element. Say you also use >> https://github.com/duffelhq/paginator for infinite scrolling pages you >> might end up with yet another "collection" type struct, which implements >> Enumerable so displaying items in views is super easy, but with no simple >> solution on how to handle preloads or mappings. >> >> I've also tried using `Map.update!(elements, :key_of_items, function)` to >> normalize stuff down to handling lists for those places using pagination, >> but now I'm wrapping a lot of computation in those updates. >> >> It's also not just mapping, but I might also e.g. want to intersperse >> items with separators or zip some additional data into the resultset and >> still not lose the pagination information attached to those entries. >> >> My naive approach was that I can already use Collectable to fill items >> back into lists as well as those pagination structs, but while for list and >> maps it's easy to use `Enum.into([])` or `Enum.into(%{})` it's not as easy >> to get a hold of an empty version of one of those pagination structs. >> >> I'm not super into all the theoretic types in functional programming. I >> think I understand what a functor is, but I'm also not super certain I >> understand what you're pointing at. >> >> Am Dienstag, 21. Mai 2019 18:36:54 UTC+2 schrieb José Valim: >>> >>> > All the pagination libs I know for ecto return structs with additional >>> metadata besides the actual results of the db query. Currently one needs to >>> build around those structs specifically to be able to do preloads or other >>> mapping operations or one would loose the metadata. >>> >>> Can you please provide an example? I am just trying to full understand >>> the problem. :) >>> >>> > Having a `SomeProtocol.empty` protocol we could still use everything >>> provided by Enum (even with it returning a list), but have a way to replace >>> items in the container with the new modified ones >>> >>> Wouldn't a functor be better suited then? >>> >>> >>> *José Valim* >>> www.plataformatec.com.br >>> Skype: jv.ptec >>> Founder and Director of R&D >>> >>> >>> On Tue, May 21, 2019 at 6:34 PM Benjamin Milde <[email protected]> >>> wrote: >>> >>>> All the pagination libs I know for ecto return structs with additional >>>> metadata besides the actual results of the db query. Currently one needs to >>>> build around those structs specifically to be able to do preloads or other >>>> mapping operations or one would loose the metadata. Having a >>>> `SomeProtocol.empty` protocol we could still use everything provided by >>>> Enum (even with it returning a list), but have a way to replace items in >>>> the container with the new modified ones without manually pattern matching >>>> between single results, lists of results or structs returned because one >>>> happens to be using pagination. Monadic collection types basically don't do >>>> it much differently. Extract the subject out of the container, do >>>> computation and replace the old value when done. I'd imagine `Enumerable` >>>> and the potential `SomeProtocol` would solve a lot of usecases, where >>>> people usually ask for Enum to retain the outer collection type. >>>> >>>> Am Dienstag, 21. Mai 2019 18:14:49 UTC+2 schrieb José Valim: >>>>> >>>>> My concern is that Collectable.empty cannot be implemented by all >>>>> structs. For example, what does it mean to call empty() on a IO.stream? >>>>> Perhaps it would make sense as a separate protocol? >>>>> >>>>> Also, can you please expand on how Repo.preload could use >>>>> Scrivener.Page in detail? Thanks! >>>>> >>>>> >>>>> *José Valim* >>>>> www.plataformatec.com.br >>>>> Skype: jv.ptec >>>>> Founder and Director of R&D >>>>> >>>>> >>>>> On Tue, May 21, 2019 at 5:46 PM Benjamin Milde <[email protected]> >>>>> wrote: >>>>> >>>>>> I've had quite often needs for doing some computation (mapping) on >>>>>> ecto result, but having a flexible function similar to `Repo.preload` >>>>>> currently needs a whole bunch of boilerplate in terms of differenciating >>>>>> collections from single items and especially returning the same type >>>>>> afterwards (e.g. keep it a collection or single item). I know that >>>>>> Enumerable and Collectable were split consciously, but it would be great >>>>>> to >>>>>> have something like `Collectable.empty/1`, so one could do some work >>>>>> using >>>>>> `Enum` functions and in the end do: `Enum.into(changed, >>>>>> Collectable.empty(initial))` and it would empty the collectable and fill >>>>>> it >>>>>> up again using the changed data. This way the `Repo.preload` could e.g. >>>>>> additionally support custom enumerable and collectable collections as >>>>>> first >>>>>> argument like e.g. `%Scrivener.Page{}`. >>>>>> >>>>>> -- >>>>>> You received this message because you are subscribed to the Google >>>>>> Groups "elixir-lang-core" group. >>>>>> To unsubscribe from this group and stop receiving emails from it, >>>>>> send an email to [email protected]. >>>>>> To view this discussion on the web visit >>>>>> https://groups.google.com/d/msgid/elixir-lang-core/19c24b83-fc2a-4af3-950e-eba7f767db14%40googlegroups.com >>>>>> <https://groups.google.com/d/msgid/elixir-lang-core/19c24b83-fc2a-4af3-950e-eba7f767db14%40googlegroups.com?utm_medium=email&utm_source=footer> >>>>>> . >>>>>> For more options, visit https://groups.google.com/d/optout. >>>>>> >>>>> -- >>>> You received this message because you are subscribed to the Google >>>> Groups "elixir-lang-core" group. >>>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to [email protected]. >>>> To view this discussion on the web visit >>>> https://groups.google.com/d/msgid/elixir-lang-core/1498525e-30fd-4cde-92a0-4b2e01cdbdf3%40googlegroups.com >>>> <https://groups.google.com/d/msgid/elixir-lang-core/1498525e-30fd-4cde-92a0-4b2e01cdbdf3%40googlegroups.com?utm_medium=email&utm_source=footer> >>>> . >>>> For more options, visit https://groups.google.com/d/optout. >>>> >>> -- >> You received this message because you are subscribed to the Google Groups >> "elixir-lang-core" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/elixir-lang-core/5dff9895-1921-4794-89b9-d4ff45578880%40googlegroups.com >> <https://groups.google.com/d/msgid/elixir-lang-core/5dff9895-1921-4794-89b9-d4ff45578880%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> For more options, visit https://groups.google.com/d/optout. >> > -- > You received this message because you are subscribed to a topic in the > Google Groups "elixir-lang-core" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/elixir-lang-core/3iBUmpKIYr8/unsubscribe > . > To unsubscribe from this group and all its topics, send an email to > [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/elixir-lang-core/CAGnRm4Kueg013YTHmg7jS5o94Qb0YbEjOWRNbKuENKgPiMJK0g%40mail.gmail.com > <https://groups.google.com/d/msgid/elixir-lang-core/CAGnRm4Kueg013YTHmg7jS5o94Qb0YbEjOWRNbKuENKgPiMJK0g%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > For more options, visit https://groups.google.com/d/optout. > > -- > You received this message because you are subscribed to the Google Groups > "elixir-lang-core" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/elixir-lang-core/DEDD7A1D-7CBD-4EC9-82B0-2C597DC8CC85%40kobrakai.de > <https://groups.google.com/d/msgid/elixir-lang-core/DEDD7A1D-7CBD-4EC9-82B0-2C597DC8CC85%40kobrakai.de?utm_medium=email&utm_source=footer> > . > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "elixir-lang-core" group. 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