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?
Where Next?
Trending in Questions
Other Trending Topics
Latest on Elixir Forum
Sponsor Spotlight
Practical resources that improve the lives of professional developers.
Categories:
Sub Categories:
Forums
Popular Tags
- #ecto
- #liveview
- #troubleshooting
- #learning-elixir
- #library
- #deployment
- #erlang
- #testing
- #genserver
- #mix
- #absinthe
- #remote-other
- #otp
- #plug
- #how-to-question
- #macros
- #postgres
- #elixirconf
- #channels
- #exunit
- #discussion
- #code-sync
- #podcasts
- #javascript
- #onsite
- #dialyzer
- #docker
- #authentication
- #umbrella
- #full-time-contract
- #ai
- #podcasts-by-brainlid
- #ecto-query
- #elixirconf-us
- #blog-post
- #elixir-ls
- #phoenix_html
- #iex
- #graphql
- #genstage
- #websockets
- #supervisor
- #advent-of-code
- #distillery
- #processes
- #elixirconf-eu
- #api
- #forms
- #security
- #metaprogramming
Our Sponsors
Build Elixir applications with speed and confidence.
Supporting innovation across the BEAM ecosystem.
Catch errors, track performance, monitor hosts and more.
Error tracking, logs, uptime, and Just Enough APM. Built for developers.
Elixir, Erlang & BEAM conferences from Code Sync - join us in 2026!
Practical resources that improve the lives of professional developers.
Master modern tools, write cleaner code, and tackle real-world challenges.
Bringing learning, work and compliance together since 1987.
The team behind Membrane, Popcorn, LiveDebugger. Available for hire.
Courses that'll move you from confusion to "Aha, now I get it!"
Showing Posts 1 to 7- Show Best Posts
- Show All (oldest first)
- Show All (newest first)
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!.