lessless
I wonder if it’s possible to mimic a simple “class reopening”/inhertinace-based SEAM in Elixir to alter a module’s behaviour without editing its code.
Here is an example in pseudo-Ruby
class PriceCalculator
def calculate_price(order)
base_price = calculate_base_price(order)
shipping = calculate_shipping(order)
base_price + shipping
end
def calculate_shipping(order)
ShippingServices.calculate_shipping(order)
end
end
Now the calculate_shipping is enabling point to override the shipping costs calculation behaviour because we can override it in tests without altering the production code.
class Test
class PriceCalculatorStub < Price calculator
def calculate_shipping(order)
1000
end
end
def test_order_price_is_base_price_plus_shipping_price
assert 1100 == PriceCalculatorStub.new.calculate_price(...)
end
end
Example is adapted from Legacy Seam
Where Next?
Trending in Discussions
Other Trending Topics
Latest on Elixir Forum
Sponsor Spotlight
Build Elixir applications with speed and confidence.
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
- #podcasts-by-brainlid
- #ecto-query
- #ai
- #elixirconf-us
- #blog-post
- #elixir-ls
- #phoenix_html
- #iex
- #graphql
- #genstage
- #websockets
- #supervisor
- #advent-of-code
- #distillery
- #processes
- #api
- #forms
- #elixirconf-eu
- #metaprogramming
- #hex
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!
Master modern tools, write cleaner code, and tackle real-world challenges.
Bringing learning, work and compliance together since 1987.
Producing high quality Elixir screencasts since 2017.
The team behind Membrane, Popcorn, LiveDebugger. Available for hire.
Courses that'll move you from confusion to "Aha, now I get it!"
Showing Posts 20 to 11- Show Best Posts
- Show All (oldest first)
- Show All (newest first)
yordisprieto
lessless
Thanks for the feedback on the patch @yordisprieto. It would be nice to see the error, indeed.
@Hermanverschooten does Mimic work with private functions?
yordisprieto
We encountered some indeterministic failures from
patch, the error is about some supervisor stopping or crashing from the package (if I come across again I will update here)Aside from that, it is very difficult to find the proper interface of a module since there is no behaviour to implement. Sometimes, leading to very messy code and monkey patching way too high instead of closer to where the dependency needs to actually change. Monkey patching randomly just because they can.
Personally, I would avoid
patchpackage and stick toMoxor anything similar that requires to define a behaviour/interface for the dependencies.dimitarvp
I am mostly using Mimic and I love it, though I believe Efx is amazing but didn’t have the opportunity to use it yet.
Hermanverschooten
or Mimic
Blond11516
You might want to look at patch, which lets you mock functions without behaviours or DI.
sodapopcan
There’s also Efx. It’s a cool library. Personally I found myself going back to Mox, though (not that that matters).
Zurga
You can “patch” the code of a module by decompiling it into Erlang Abstract Format, then do any changes and then recompile the module. You can also namespace it this way.
I implemented it here: punkix/lib/punkix/patcher.ex at master · Zurga/punkix · GitHub
Example usage is here: punkix/lib/mix/tasks/punkix/gen.live.ex at master · Zurga/punkix · GitHub
Eiji
Of course OOP in
Elixirwould not work, but there are few things that looks similar and use metaprogramming to achieve similar results:D4no0
Unless you are working alone, I would highly suggest to not go that route. What you think it’s ergonomic and correct, might not fit well with folk coming from other ecosystems, so you will be creating a friction point to just avoid having to write a few lines of code.