mudasobwa
Prior to v1.18.0 I used the following vode to reach the struct definition in a module from __before_compile__/2 callback.
defp fields(module) do
module
|> Module.get_attribute(:__struct__, %{})
|> Map.delete(:__struct__)
|> Map.keys()
end
I know that’s the undocumented, internal feature, but I did not manage to find a better way of doing this. In v1.18.0 this :__struct__ module attribute has gone. By digging down the rabbit hole, I managed to do the following:
defp fields(module) do
with {set, _bag} <- module |> :elixir_module.data_tables(),
true <- :ets.member(set, {:elixir, :struct}),
[{{:elixir, :struct}, [_ | _] = fields}] <- :ets.lookup(set, {:elixir, :struct}) do
for %{field: field} <- fields, do: field
end
end
While it works, it looks extremely hacky and might break again tomorrow. Is there the correct way of doing that that I am missing?
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LostKobrakai
I’d unimport
Kerner.defstruct, import your own wrapper (I expect you have ause MyModule) and have it persist the information you need in a way your before compile callback can access the information.mudasobwa
I hate to imply limitations like “you must
use This” before calling a standard library macrodefstruct/1onto the user. I expect the code below to work smoothlyIn any case, I expect to be able to get a struct definition from the
__before_compile__/2callback, and I find the necessity to hack it quite disturbing.dimitarvp
Apologies for a likely uninformed question but don’t compilation tracers give you what you need? One of them is this:
LostKobrakai
That might be the new way to go then based on the changelog.
mudasobwa
Thanks a ton! I must have been reading the changelog without a brain involved.
mudasobwa
Sure they would, but attaching a tracer to get a list of struct keys looks like an overkill to me.
josevalim
And if you need to support previous versions, there is
Macro.struct!.