Where is source code of `record/2` macro?

Questions / Help
1

Record documentation mentions special record/2 macro for use in typespecs only:

Types can be defined for tuples with the record/2 macro (only available in typespecs).

But I can’t find source code of this macro.
I write Record-like module and I need to write a macro to generate typescpecs.
But I don’t understand how to write a macro that would work in typespecs.

2

The implementation starts here I think, but it’s not a separate macro: elixir/typespec.ex at master · elixir-lang/elixir · GitHub

3

Thanks. So actually it’s not a macro. It is sad.

4

Do you need something like this?

defmodule TypespecMacro.Util do
  defmacro deftype(name, spec) do
    quote do
      @type unquote(name) :: unquote(spec)
    end
  end
end

defmodule TypespecMacro do
  import TypespecMacro.Util

  deftype(type1, any)
  deftype(type2, any)

  @spec foo(type1, type2) :: {type1, type2}
  def foo(arg1, arg2) do
    {arg1, arg2}
  end
end

$ iex -S mix
Erlang/OTP 23 [erts-11.1.3] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [hipe]

Interactive Elixir (1.11.2) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> h TypespecMacro.foo

                              def foo(arg1, arg2)                               

  @spec foo(type1(), type2()) :: {type1(), type2()}
5

No. I want something like this:

defmodule TypespecMacro.Util do
  defmacro defspec(fields) do
    quote do
      # generating spec based on fields
    end
  end
end

defmodule TypespecMacro do
  import TypespecMacro.Util

  @type t() :: defspec(field1: integer(), field2: String.t())
end

I already did it in the same way as in your example. Awkward, but works.

6

Good. But why awkward?

7

It is just my biased opinion.
For me

@type t() :: defspec(field1: integer(), field2: String.t())

looks better than

deftype(t, field1: integer(), field2: String.t())
8

Oh… you were referring to that. Actually, your way is the way to go, because you can define types of any arity.

9

Could you please explain what are

types of any arity

10

Well, if you wanted to define in my example a type of arity > 0 you wouldn’t have been able to do it.
By arity i mean, that it takes let’s say one argument.
@type my_type(any) :: {:ok, any()}

But doing it your way, it is possible.

11

You can use additional macro parameter:

defmacro deftype(t, params \\ [], spec) when is_list(params) do
  ...
end

deftype(t1, {:ok, any()})
deftype(t2, [any(), integer()], {:ok, &1, &2})