Fl4m3Ph03n1x
How to use anonymous functions in configuration files?
Background
I have a configuration file called test.exs that does not work because it has an anonymous function:
# stub for fire function
config :my_aop,
fire: fn(_pool_name, _endpoint) -> {:ok, :received} end
And it generates the following error:
** (ArgumentError) cannot inject attribute @default into function/macro because cannot escape #Function<12.128620087/2 in :erl_eval.expr/5>. The supported values are: lists, tuples, maps, atoms, numbers, bitstrings, PIDs and remote functions in the format &Mod.fun/arity
(elixir) lib/kernel.ex:2879: Kernel.do_at/5
(elixir) expanding macro: Kernel.@/1
lib/bidtor/dispatcher.ex:36: Bidtor.Dispatcher.send/2
(elixir) lib/kernel/parallel_compiler.ex:208: anonymous fn/4 in Kernel.ParallelCompiler.spawn_workers/6
Questions
- Can I not use anonymous functions in config files? (Is there a way this can be achieved or is it simply impossible?)
- How can I stub the given function if I cannot use anonymous functions in the configuration files?
Marked As Solved
stefanluptak
AFAIK it’s not possible to store anonymous functions in the config file, but I was not able to find more info quickly.
But it’s solvable. Put the logic into a module. Then put your “testing” logic into another module. Then just use the config to determine which module you want to use.
defmodule YourModule do
def your_function(pool_name, endpoint) do
# some real logic
end
end
defmodule YourModuleMock do
def your_function(_pool_name, _endpoint) do
{:ok, :received}
end
end
test.exs:
config :my_aop, fire: YourModuleMock
usage:
module = Application.get_env(:my_aop, :fire, YourModule)
module.your_function(param1, param2)
Also Liked
peerreynders
You may also want to borrow this from a typical Phoenix project.
In mix.exs:
def project do
[
app: :form_demo,
version: "0.1.0",
elixir: "~> 1.5",
elixirc_paths: elixirc_paths(Mix.env()),
compilers: [:phoenix, :gettext] ++ Mix.compilers(),
start_permanent: Mix.env() == :prod,
deps: deps()
]
end
]
In particular elixirc_paths. The elixirc_paths/1 function returns the compilation paths based on the mix environment. Further down:
# Specifies which paths to compile per environment.
defp elixirc_paths(:test), do: ["lib", "test/support"]
defp elixirc_paths(_), do: ["lib"]
So for :test test/support is added to the compilation path. So all .ex files only used for testing go under test/support and those modules are then available for all the .exs testing scripts.
In combination with values set in config.exs and compile time use of Application.fetch_env!/2 the appropriate module can then be selected (example).
Popular in Questions
Other popular topics
Latest on Elixir Forum
Sponsor Spotlight
Enabling companies to succeed by building software people love.
Categories:
Sub Categories:
Forums
Our Sponsors
Build Elixir applications with speed and confidence.
Supporting innovation across the BEAM ecosystem.
We build reliable cloud platforms for business-critical systems.
Catch errors, track performance, monitor hosts and more.
Develop your skills with books, videos, and courses.
Producing high quality Elixir screencasts since 2017.
The deployment platform built for Elixir: PaaS ease, VPS control.
Courses that'll move you from confusion to "Aha, now I get it!"