alias/2 is used to set up aliases, often useful with modules' names.

Examples

alias/2 can be used to set up an alias for any module:

defmodule Math do
  alias MyKeyword, as: Keyword
end

In the example above, we have set up MyKeyword to be aliased as Keyword. So now, any reference to Keyword will be automatically replaced by MyKeyword.

In case one wants to access the original Keyword, it can be done by accessing Elixir:

Keyword.values #=> uses MyKeyword.values
Elixir.Keyword.values #=> uses Keyword.values

Note that calling alias without the :as option automatically sets an alias based on the last part of the module. For example:

alias Foo.Bar.Baz

Is the same as:

alias Foo.Bar.Baz, as: Baz

We can also alias multiple modules in one line:

alias Foo.{Bar, Baz, Biz}

Is the same as:

alias Foo.Bar
alias Foo.Baz
alias Foo.Biz

Lexical scope

import/2, require/2 and alias/2 are called directives and all have lexical scope. This means you can set up aliases inside specific functions and it won't affect the overall scope.

Warnings

If you alias a module and you don't use the alias, Elixir is going to issue a warning implying the alias is not being used.

In case the alias is generated automatically by a macro, Elixir won't emit any warnings though, since the alias was not explicitly defined.

Both warning behaviours could be changed by explicitly setting the :warn option to true or false.