diff --git a/erfa_generator.py b/erfa_generator.py
index 32ec0a7..31159e1 100644
--- a/erfa_generator.py
+++ b/erfa_generator.py
@@ -13,7 +13,7 @@
 import functools
 import re
 from pathlib import Path
-from typing import Final
+from typing import Final, final
 
 DEFAULT_ERFA_LOC = Path(__file__).with_name("liberfa") / "erfa" / "src"
 DEFAULT_TEMPLATE_LOC = Path(__file__).with_name("erfa")
@@ -130,14 +130,66 @@ def __init__(self, doc):
 
 class Variable:
     """Properties shared by Argument, Return and StatusCode."""
+
+    def __init__(self, ctype: str, name: str | None = None) -> None:
+        self.ctype: Final = ctype
+        self.name: Final = "c_retval" if name is None else name
+
+    @final
     @property
-    def npy_type(self):
+    def npy_type(self) -> str:
         """Predefined type used by numpy ufuncs to indicate a given ctype.
 
         Eg., NPY_DOUBLE for double.
         """
         return "NPY_" + self.ctype.upper()
 
+    @property
+    def dtype(self) -> str:
+        return "dt_" + self.ctype
+
+    @property
+    def signature_shape(self) -> str:
+        return "()"
+
+
+class Argument(Variable):
+    def __init__(self, definition: str, doc: FunctionDoc) -> None:
+        self.doc = doc
+        ctype, ptr_name_arr = definition.strip().rsplit(" ", 1)
+        name_arr = ptr_name_arr.removeprefix("*").removesuffix("[]")
+        self.is_ptr = name_arr != ptr_name_arr
+        if "[" in name_arr:
+            name_arr, arr = name_arr.split("[", 1)
+            self.shape = tuple([int(size) for size in arr[:-1].split("][")])
+        else:
+            self.shape = ()
+        super().__init__(ctype, name_arr)
+
+    @functools.cached_property
+    def inout_state(self) -> str:
+        inout_state = ""
+        for i in self.doc.input:
+            if self.name in i.name.split(","):
+                inout_state = "in"
+        for o in self.doc.output:
+            if self.name in o.name.split(","):
+                inout_state = "inout" if inout_state == "in" else "out"
+        return inout_state
+
+    @property
+    def name_for_call(self) -> str:
+        """How the argument should be used in the call to the ERFA function.
+
+        This takes care of ensuring that inputs are passed by value,
+        as well as adding back the number of bodies for any LDBODY argument.
+        The latter presumes that in the ufunc inner loops, that number is
+        called 'nb'.
+        """
+        if self.ctype == "eraLDBODY":
+            return "nb, _" + self.name
+        return ("_" if self.is_ptr else "*_") + self.name
+
     @property
     def dtype(self):
         """Name of dtype corresponding to the ctype.
@@ -173,7 +225,7 @@ def dtype(self):
             case "double", (2,):
                 return "dt_pvdpv"
             case _, ():
-                return "dt_" + self.ctype
+                return super().dtype
         raise ValueError(f"ctype {self.ctype} with shape {self.shape} not recognized.")
 
     @property
@@ -215,54 +267,13 @@ def signature_shape(self):
                 return "(3)"
             case "double", (3, 3):
                 return "(3, 3)"
-        return "()"
-
-
-class Argument(Variable):
-
-    def __init__(self, definition, doc):
-        self.doc = doc
-        self.ctype, ptr_name_arr = definition.strip().rsplit(" ", 1)
-        name_arr = ptr_name_arr.removeprefix("*").removesuffix("[]")
-        self.is_ptr = name_arr != ptr_name_arr
-        if "[" in name_arr:
-            self.name, arr = name_arr.split("[", 1)
-            self.shape = tuple([int(size) for size in arr[:-1].split("][")])
-        else:
-            self.name = name_arr
-            self.shape = ()
-
-    @functools.cached_property
-    def inout_state(self):
-        inout_state = ""
-        for i in self.doc.input:
-            if self.name in i.name.split(","):
-                inout_state = "in"
-        for o in self.doc.output:
-            if self.name in o.name.split(","):
-                inout_state = "inout" if inout_state == "in" else "out"
-        return inout_state
-
-    @property
-    def name_for_call(self):
-        """How the argument should be used in the call to the ERFA function.
-
-        This takes care of ensuring that inputs are passed by value,
-        as well as adding back the number of bodies for any LDBODY argument.
-        The latter presumes that in the ufunc inner loops, that number is
-        called 'nb'.
-        """
-        if self.ctype == 'eraLDBODY':
-            return 'nb, _' + self.name
-        return ("_" if self.is_ptr else "*_") + self.name
+        return super().signature_shape
 
 
 class StatusCode(Variable):
     def __init__(self, ctype: str, doc: FunctionDoc, funcname: str) -> None:
-        self.name = "c_retval"
         self.inout_state = "stat"
-        self.ctype = "int"
-        self.shape = ()
+        super().__init__(ctype)
 
         status = re.search(
             r"Returned \(function value\):\n\s+\w+\s+status.*?:(.+?)\s+Notes?:",
@@ -291,10 +302,8 @@ def to_python(self) -> str:
 class Return(Variable):
 
     def __init__(self, ctype, doc):
-        self.name = 'c_retval'
         self.inout_state = "ret"
-        self.ctype = ctype
-        self.shape = ()
+        super().__init__(ctype)
 
 
 class Function: