”Use“ and some metaprograming to refactor behaviours implimentation

lib/iban_ex/country/template.ex

@@ -1,4 +1,6 @@
 defmodule IbanEx.Country.Template do
+  @moduledoc false
+
   alias IbanEx.Iban
   @type size() :: non_neg_integer()
   @type rule() :: Regex.t()
@@ -7,6 +9,41 @@ defmodule IbanEx.Country.Template do
 
   @callback size() :: size()
   @callback rule() :: rule()
-  @callback to_s(Iban.t(), joiner()) :: String.t()
-  @callback to_s(Iban.t()) :: String.t()
+  @callback to_string(Iban.t(), joiner()) :: String.t()
+  @callback to_string(Iban.t()) :: String.t()
+
+  defmacro __using__(_opts) do
+    quote do
+      alias IbanEx.Iban
+      @behaviour IbanEx.Country.Template
+
+      @impl IbanEx.Country.Template
+      @spec to_string(Iban.t()) :: binary()
+      @spec to_string(Iban.t(), binary()) :: binary()
+      def to_string(
+            %Iban{
+              country_code: country_code,
+              check_digits: check_digits,
+              bank_code: bank_code,
+              branch_code: _branch_code,
+              national_check: _national_check,
+              account_number: account_number
+            } = _iban,
+            joiner \\ " "
+          ) do
+        [country_code, check_digits, bank_code, account_number]
+        |> Enum.join(joiner)
+      end
+
+      @impl IbanEx.Country.Template
+      @spec size() :: Integer.t()
+      def size(), do: @size
+
+      @impl IbanEx.Country.Template
+      @spec rule() :: Regex.t()
+      def rule(), do: @rule
+
+      defoverridable to_string: 1, to_string: 2, size: 0, rule: 0
+    end
+  end
 end