Friendlier record accessors

implementations/python/preserves/preserves.py

@@ -97,6 +97,17 @@ class Record(object):
         ctor.constructorInfo = RecordConstructorInfo(label, arity)
         ctor.isClassOf = lambda v: \
                          isinstance(v, Record) and v.key == label and len(v.fields) == arity
+        def ensureClassOf(v):
+            if not ctor.isClassOf(v):
+                raise TypeError("Record: expected %r/%d, got %r" % (label, arity, v))
+            return v
+        ctor.ensureClassOf = ensureClassOf
+        for fieldIndex in range(len(fieldNames)):
+            fieldName = fieldNames[fieldIndex]
+            # Stupid python scoping bites again
+            def getter(fieldIndex):
+                return lambda v: ensureClassOf(v)[fieldIndex]
+            setattr(ctor, '_' + fieldName, getter(fieldIndex))
         return ctor
 
 class RecordConstructorInfo(object):

implementations/python/preserves/test_preserves.py

@@ -204,3 +204,18 @@ class CodecTests(unittest.TestCase):
         self._roundtrip(SequenceStream([StringStream([b'abc']), StringStream([b'def'])]),
                         _buf(0x2C, 0x25, 0x63, 'abc', 0x35, 0x25, 0x63, 'def', 0x35, 0x3C),
                         back=(u'abc', u'def'))
+
+class RecordTests(unittest.TestCase):
+    def test_getters(self):
+        T = Record.makeConstructor('t', 'x y z')
+        T2 = Record.makeConstructor('t', 'x y z')
+        U = Record.makeConstructor('u', 'x y z')
+        t = T(1, 2, 3)
+        self.assertTrue(T.isClassOf(t))
+        self.assertTrue(T2.isClassOf(t))
+        self.assertFalse(U.isClassOf(t))
+        self.assertEqual(T._x(t), 1)
+        self.assertEqual(T2._y(t), 2)
+        self.assertEqual(T._z(t), 3)
+        with self.assertRaises(TypeError):
+            U._x(t)

implementations/python/setup.py

@@ -5,7 +5,7 @@ except ImportError:
 
 setup(
     name="preserves",
-    version="0.0.4",
+    version="0.0.5",
     author="Tony Garnock-Jones",
     author_email="tonyg@leastfixedpoint.com",
     license="GNU General Public License v3 or later (GPLv3+)",