Why are module names in Elixir UpperCamelCase, while the file names are snake_case?

It’s just convention. This is how Ruby does it which of course inspired a lot of Elixir conventions. Also, Erlang modules names are conventionally snake case (and at least must start with a lowercase letter). There is no technical reason, but one thing to keep in mind is that file != module in Elixir, ie, you can have multiple modules in a single file. I often have some files that aren’t named after any of the contained modules, like errors.ex. For me (and this is just me), using camel case would suggest that the file is the module whereas snake case more correctly suggests there is no such correlation

Not all filesystems are case-sensitive, so trying to camel-case there will give you files with unwieldylongnameswithoutanypunctuation

I suspect that constraint in Elixir may have been more about “why are Ruby files named like this” and then migrated over, but I don’t have any evidence for that.

While it’s true much of Elixir’s syntax was inspired by Ruby, the root of it is almost certainly as @al2o3cr mentioned - not all file systems are case sensitive.

Then why is it such a prevalent convention in JavaScript? Also, BEAM files maintain the module name’s casing.

No idea - maybe the creator’s of Ruby wanted to maintain compatibility with those systems?

For file systems that are not case-sensitive these would be the same:

TestsCase
TestScase

Haven’t watched it, but this might be worth a watch:

Oh ya, I get the case-sensitive thing, I’m just asking—semi-rhetorically—why JS does if it can cause such problems. When it comes to source file naming, I’ve never been a fan of anything other than all lower snake or kebab case. I have a personal preference for kebab, but since Elixir doesn’t support kebab identifiers, I’m happy with snake.

EDIT: Oops, I think you understood this

@ulissesalmeida I hope this post gives you the valuable information you were looking for, all those years back when you were writing the article.

If you found out something else that we don’t know, feel free to let us know!
I hope this thread finds you well and puts that pesky question to an end !

Well something that no one has mentioned to this point; module names are also atoms. Therefore they must start with an uppercase letter. Hence I think it makes some sense to use camel case on module names simply to ease comprehension.

Nitpick for clarity: module names are aliases which is why they must start with an uppcase letter. And to nitpick myself, of course you can use straight up atoms as well, ie defmodule :foo, do: (). But yes, always atoms.

Excellent point. Hairsplitting may be unwelcome in other arenas but in software development it’s essential!