sodapopcan
I apologize if this has been discussed before, and I’m sure it probably has been, but it’s very hard to search for. I’ve been putting off asking about it for a while now, though, so I’m curious about this pattern:
_ = SomeMod.some_func("some_arg")
I’ve seen this in the docs before but the most prominent example I know of is the first two lines of the first function definition in Phoenix, here. If you aren’t a fan of clicking it looks like this:
# Warm up caches
_ = Phoenix.Template.engines()
_ = Phoenix.Template.format_encoder("index.html")
The best explanation I can come up with is that it’s signalling a side-effect. Is that it?? If it is, I find that kind of really nice, although perhaps at the same time it’s warmed me up a bit to typing (in Elixir) as it took me way to long to figure that out, lol.
But really, it is that it? If not, what’s up with this?
Where Next?
Trending in Discussions
Other Trending Topics
Latest on Elixir Forum
Sponsor Spotlight
Error tracking, logs, APM, uptime and cron monitoring in one dev-friendly platform. Find and fix problems before your users notice.
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
- #ai
- #ecto-query
- #elixirconf-us
- #blog-post
- #elixir-ls
- #phoenix_html
- #iex
- #graphql
- #genstage
- #websockets
- #supervisor
- #advent-of-code
- #distillery
- #processes
- #elixirconf-eu
- #api
- #forms
- #metaprogramming
- #hex
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.
Elixir, Erlang & BEAM conferences from Code Sync - join us in 2026!
Practical resources that improve the lives of professional developers.
Producing high quality Elixir screencasts since 2017.
**Building the future of software with AI, trust, and human connection.**
The team behind Membrane, Popcorn, LiveDebugger. Available for hire.
Courses that'll move you from confusion to "Aha, now I get it!"
Most Liked- Show Best Posts
- Show All (oldest first)
- Show All (newest first)
LostKobrakai
To focus the discussion. The warnings come from an (optional) dialyzer setting. That‘s why this approach is not present in all codebases, but just some.
hauleth
Yeah, I often use such pattern to mark that I run that piece of code for sole purpose of side effects and I do not care about return value. So it will not be perceived as unintentional omission, but deliberate choice of ignoring returned values.
eksperimental
It was probably to avoid so kind of generated warning. If i see function that is not assigned or matched to anything I would assume it has a side effect, so I would not see the need for
_ =.