I wish I could edit my messages here :) But passing a user's module to a library is really common (I had not had my first coffee yet...). Just looking at the config file should be enough.
For example: `config :elixir, :time_zone_database, Tz.TimeZoneDatabase` Don't we want to make sure that the module I pass (`Tz.TimeZoneDatabase`) implements the `Calendar.TimeZoneDatabase` behaviour? And raise if that's not the case. Or that the Repo I pass in the config is a valid Repo? Et cetera. For example I changed in my config file module `Tz.TimeZoneDatabase` by `Foo`. And there is no error. Only when I call something like: `DateTime.shift_zone(~U[2018-07-16 10:00:00Z], "America/Los_Angeles")` I will get the error: `** (UndefinedFunctionError) function Foo.time_zone_period_from_utc_iso_days/2 is undefined (module Foo is not available)` In my library I would add a function such as `raise_unless_implements/2` to make sure that the custom module behaves as expected. I'm now surprised that this isn't a common practice. On Monday, May 18, 2020 at 2:26:10 AM UTC+2, Thomas J. wrote: > > Hello Andrea! > > Imagine, as a library author, that a library module can somehow receive a > module from your application to call functions on. > > E.g. `use LibraryModule, yourModule: Foo` > > `LibraryModule` expect to receive in its `:yourModule` option a module > implementing a certain behaviour. `Foo` is given and the library code wants > to raise an error if the given module doesn't implement the expected > behaviour. > > Actually I thought, that should be pretty common. So I checked in the > dependencies containing large amount of code and configs such as Phoenix, > Ecto, Absinthe, and so on, and guess what, this pattern is almost not > used... > > I still found this: > https://hexdocs.pm/ecto/Mix.Ecto.html#ensure_implements/3 > > > On Sunday, May 17, 2020 at 5:15:08 PM UTC+2, Andrea Leopardi wrote: >> >> Hey Thomas, >> >> do you have a specific use case in mind to check that a module implements >> a behaviour? The fact that you can do this today by getting the module >> attributes makes me lean towards not adding this to the standard library, >> but I'm curious as to that's the use case you're thinking of :) >> >> Andrea >> >> On Sun, May 17, 2020 at 10:41 AM Thomas J. <thojan...@gmail.com> wrote: >> >>> Hello, >>> >>> What do you think about adding `implements?/2`? >>> >>> It accepts two module names as parameters, and it checks if the first >>> parameter implements the behaviour passed as the second parameter. >>> >>> It would execute something like: >>> >>> `Enum.member?(Foo.module_info[:attributes][:behaviour], Bar)` >>> >>> Only problem I see is that a module can somehow implement a behaviour >>> without wriring the @behaviour statement. But that could be a documented >>> limitation. >>> >>> >>> -- >>> 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 elixir-l...@googlegroups.com. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/elixir-lang-core/12b5fbff-7460-44c1-81c1-b6710949738e%40googlegroups.com >>> >>> <https://groups.google.com/d/msgid/elixir-lang-core/12b5fbff-7460-44c1-81c1-b6710949738e%40googlegroups.com?utm_medium=email&utm_source=footer> >>> . >>> >> -- 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 elixir-lang-core+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/elixir-lang-core/bd8b2a59-a5e2-4e94-a4f3-bcf22fa8e3d3%40googlegroups.com.
