Greetings comrades, According to: https://elixir-lang.org/getting-started/module-attributes.html#as-constants Every time an attribute is read inside a function, Elixir takes a snapshot of its current value. My question is: In this function: @money %{amount: 0, currency: :DOGE} def reset_glob…

Here’s the code. you can clone it GitHub - eksperimental-help/slouchpie · GitHub Unoptimized: slouchpie/lib/foo_big.ex at main · eksperimental-help/slouchpie · GitHub Optimized: slouchpie/lib/foo_small.ex at main · eksperimental-help/slouchpie · GitHub $ mix compile $ touch lib/foo_big.ex && rm…

No. The value is basically a static constant, and in fact won’t even take up memory in the process like a normal map, since it will be just a pointer to the shared constant pool.

Yes, the runtime memory is unaffected. I’m wondering if there are 2 copies during compile time. The same article says: Therefore if you read the same attribute multiple times inside multiple functions, you may end-up making multiple copies of it. That’s usually not an issue, but if you are using…

It is as if you hand typed that map in two places. This can affect compile times, but it generally requires very large constants to be an issue.

To add onto the previous answer. The cost occurs when you make a change. The following would be calculated twice. If we were doing expensive or numerous changes, it would affect the time taken to compile @var1 1+1 @var1 1+2

@benwilson512 as a tangent here, could you please teach me how to verify this? I’d love to know how.

If you can read erlang you can use mix decompile to turn your compiled module into erlang source. And you will see that whenever an @attribute is used, the litteral value is present in the source. Now if you cannot read erlang I guess you will recocgnize your own data enough to verify too.

[image] slouchpie: do 2 copies of @money get created, since it is “read” twice? the copies are inside your def. Note that it is not two copies only, but 2 times the elements of Earth.list_humans() if you don’t want to create copies, you may want want refactor your code: @money %{amount: 0…

I don’t understand this at all, sorry. How are the elements of Earth.list_humans() known at compile time?

Sorry, You are right. I was wrong about the part about 2 * number of Earth.list_humans(). It is just two copies. The rest still applies. as you save from duplicating the content of @money, and access the keys of the map for every element in list_humans at run time.

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Are module attributes "read" multiple times in same function?

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slouchpie December 14, 2021, 4:59pm 5

Perfect, thanks