Dialyzer message help

Questions / Help
1

Hi, can you please help me understand this one?

The call 'Elixir.Enrol.Classes':enroll_user
         (_enrollment_params@1 :: #{<<_:56, _:_*8>> => _}) breaks the contract 
          (#{'class_id' := integer(),
            'user_id' := integer(),
            any() => any()}) ->
             any()

I don’t understand this bit: (_enrollment_params@1 :: #{<<_:56, _:_*8>> => _})

What I am trying to say that this function expects a map with two required parameters class_id and user_id, both being integers.

The spec itself looks like this:

@spec enroll_user(%{
          :class_id => integer,
          :user_id => integer,
          optional(any) => any
        }) :: any

^ I put there return type to any for now to try to figure out my problem.

Thank you

2

The map that has only string keys does not match the expected type of a map that has at least the 2 required atom keys :class_id and :user_id.

3

Thank you. Is there a way to say the input struct must have keys “class_id” and “user_id”? I can’t seem to find or figure out the right syntax for that.

4

It’s already like that. foo: integer requires that the key :foo exists and it’s value is of type integer.

5

yes but I mean string key "class_id" rather than atom key :class_id. these are essentially params.

6

I do not remember if literal strings are allowed as key-types in a map, as they simply aren’t allowed everywhere, but if they are allowed required("foo") => any should do.

7

seems like one more tweak was needed: required(class_id :: String.t()) => pos_integer

8

Typespecs do not have the ability to specify specific string keys. Only atoms can be used as specific keys.

4 Likes
9

Which means, that there has at least one key of type string. It doesn’t say anything about the value of the string.

10

I see. I should not be getting string keys into this function in the first place, so I will refactor accordingly, and that will solve the problem, taking into account what @benwilson512 also wrote. Thank you both!