Enforcing a type spec

Questions / Help
1 
  @spec foo (arg1 :: String.t(), arg2 :: String.t(), arg3 :: float) :: float

  def foo("bing", "bang", "bow") do
      some process
  end

Is there a way to get iex to raise a type spec error for foo() when it’s executed with incorrectly typed argumens?

2

No. There are others libraries that may help you with that, but “bare” Erlang (and Elixir) do not have support for something like that.

1 Like
3

Gotcha. Which would you recommend?

4

TypeCheck is a thing, not sure if it works in IEx. That’s an interesting thought for the library I’m working on, which is compile-time type inference, so I think I’ll toss it on the issues/features list.

2 Likes
5

If you want static analysis, you can take a look at https://hexdocs.pm/dialyzex/Mix.Tasks.Dialyzer.html

1 Like
6

Typespec is just annotation and not used at runtime (like @doc).

To raise an error at runtime - you may add guard to functions so that you get no match found error. There are a few libraries to add abstraction for generating typespec and guard…

See also:

(you can see people in this thread there!)

1 Like
7

This worked out nicely:

iex(2)> Sandbox.foo("bing", "bang", "bow")
** (TypeCheck.TypeError) The call `foo("bing", "bang", "bow")` does not adhere to spec `foo(binary(),  binary(),  float()) :: float()`. Reason:
  parameter no. 3:
    `"bow"` is not a float.
    (arbit 0.1.0) lib/Sandbox.ex:1: Sandbox.foo/3