Representing IO in a spec

English3000 · May 15, 2018, 5:44pm

  @spec greeting(String.t) :: String.t
  def greeting(name \\ nil, io \\ IO) do
    # ...
  end

Per this article, I am inserting the IO module as an input to my function for testing purposes.

How do I represent this in my spec?

easco · May 15, 2018, 5:54pm

In io.ex in the Elixir source code. It appears that they use a type called device:

@type device :: atom | pid

github.com

elixir-lang/elixir/blob/master/lib/elixir/lib/io.ex#L37


IO devices maintain their position, which means subsequent calls to any
reading or writing functions will start from the place where the device
was last accessed. The position of files can be changed using the
`:file.position/2` function.


## IO data


IO data is a data type that can be used as a more efficient alternative to binaries
in certain situations.


A term of type **IO data** is a binary or a list containing bytes (integers in `0..255`)
or nested IO data. The type is recursive. Let's see an example of one of
the possible IO data representing the binary `"hello"`:


    [?h, "el", ["l", [?o]]]


The built-in `t:iodata/0` type is defined in terms of `t:iolist/0`. An IO list is
the same as IO data but it doesn't allow for a binary at the top level (but binaries
are still allowed in the list itself).


### Use cases for IO data

English3000 · May 15, 2018, 6:47pm

Appreciate your promptness!

Adding that isn’t throwing errors (it wasn’t before either, though).

Still not sure this is right, as I am passing a module made up of functions… Dialyzer would be the way to validate this?

NobbZ · May 15, 2018, 7:38pm

The type of a module name is atom().