Alias, imports, requires inside or outside the module?

[belaustegui]

Looking at the code of Elixir and Ecto core I found some files that have import, alias or require directives in multiple places.

• Some have them outside the module: https://github.com/elixir-ecto/ecto/blob/master/lib/ecto/association.ex#L1
• Some have them inside the module: https://github.com/elixir-ecto/ecto/blob/master/lib/ecto/migrator.ex#L23-L26
• And some have a mix of inside and outside: https://github.com/elixir-lang/elixir/blob/master/lib/elixir/lib/float.ex

I know that those directives are lexically scoped, but I’m afraid I don’t understand the differences between using them outside or inside the module.

What advantages/disadvantages has one form and the other? Is there a preferred way to go? When should I use one or the other?

[michalmuskala]

As you said the key is lexical scoping. Importing outside of the module makes sense only when defining multiple modules in a single file - the import at the file level will affect all the modules - that’s exactly what’s happening in the ecto associations file - this file defines multiple modules, and importing the functions over and over again would be tiring.

In case of the float module, I see no reason for extracting the import at the file level. It might be some historical left-over, or a preference to single out Kernel exclusions.

[josevalim]

Just to echo Michał’s reply, if you have a single module, there is no difference whatsoever.