I was checking the documentation for elixir and erlang types for ways to represent a map in the typespec.

I have seen different projects defining types for maps this way:

@type user :: %{
  required(:first_name) => binary(),
  optional(:last_name) => binary()
}

And this would be a valid “user” map that follows the typespec:

%{first_name: "John", last_name: "Doe"}

I could not find in the docs whats the proper way to represent a map with string keys. I tried to create a similar type from above using string keys instead of atom keys:

@type user :: %{
  required("first_name") => binary(),
  optional("last_name") => binary()
}

but this doesn’t compile, which is kinda expected considering the documentation is clear that it should follow the given format:

      | %{}                                   # empty map
      | %{key: value_type}                    # map with required key :key of value_type
      | %{key_type => value_type}             # map with required pairs of key_type and value_type
      | %{required(key_type) => value_type}   # map with required pairs of key_type and value_type
      | %{optional(key_type) => value_type}   # map with optional pairs of key_type and value_type

But feels like the language could offer some support for this type:

%{"key" => value_type}                    # map with required key "key" of value_type

So maps with string keys have better representation when defining the @type instead of fallback to map() or %{binary() => term()}.