Enumerable.count

You're seeing just the function count, go back to Enumerable module for more information.

Specs

count(t()) :: {:ok, non_neg_integer()} | {:error, module()}

Retrieves the number of elements in the enumerable.

It should return {:ok, count} if you can count the number of elements in enumerable without traversing it.

Otherwise it should return {:error, __MODULE__} and a default algorithm built on top of reduce/3 that runs in linear time will be used.