rm-rf-etc
I’m creating a custom type and I need to define original logic for the square bracket operator. How do I go about doing this? Do I use defimpl to define a protocol, or write a macro, or use Access behavior? Or some combination thereof?
Where Next?
Trending in Questions
Other Trending Topics
Latest on Elixir Forum
Sponsor Spotlight
We build reliable cloud platforms for business-critical systems.
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
- #ai
- #full-time-contract
- #podcasts-by-brainlid
- #ecto-query
- #blog-post
- #elixirconf-us
- #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.
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!
Producing high quality Elixir screencasts since 2017.
**Building the future of software with AI, trust, and human connection.**
The deployment platform built for Elixir: PaaS ease, VPS control.
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 4- Show Best Posts
- Show All (oldest first)
- Show All (newest first)
LostKobrakai
You should just need to implement the access behaviour: Access — Elixir v1.20.2
rm-rf-etc
@LostKobrakai my struct is a table, so I need the brackets to take two indices. Would I implement this using syntax like
[a][b]or[a, b]? I guess I’m still confused how behavior gets implemented. For example, let’s say I want to define access to also support a range for the index, so I could use an index (for the column) and a range for the row (to produce the enumerable for the subset of rows from the given column).rm-rf-etc
Okay, I see now that
Access.get/3is invoked when I use the square bracket, but in some cases it callsAccess.fetch/2, so I don’t get this. I was able to implementfetch/2so that I can usemy_table[{0, 0}]to get the first entry from the first column, but[0, 0]would be a lot nicer.I see this now, getting educated on how elixir works.
LostKobrakai
If you look at
put_in,update_inorpop_inthose brakets could also invoke different callbacks of the behaviour besidesfetch/2. As you’ve noticed those brackets are a way for you to supply a key to be used. That key can be any term, but as you’ve seen it needs to be one term not many.