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?
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First 4 of 4 Posts
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.