feat: improve unmarshall performance for SignatureType (#436)

src/dbus_fast/_private/unmarshaller.py

@@ -607,7 +607,7 @@ class Unmarshaller:
             )
         else:
             array_length = self._uint32_unpack(self._buf, self._pos - UINT32_SIZE)[0]
-        child_type: SignatureType = type_.children[0]
+        child_type = type_._child_0
         token_as_int = child_type.token_as_int
 
         if token_as_int in {
@@ -631,9 +631,8 @@ class Unmarshaller:
             result_dict: dict[Any, Any] = {}
             key: str | int
             beginning_pos = self._pos
-            children = child_type.children
-            child_0 = children[0]
-            child_1 = children[1]
+            child_0 = child_type._child_0
+            child_1 = child_type._child_1
             child_0_token_as_int = child_0.token_as_int
             child_1_token_as_int = child_1.token_as_int
             # Strings with variant values are the most common case

src/dbus_fast/signature.pxd

@@ -9,6 +9,8 @@ cdef class SignatureType:
     cdef public unsigned int token_as_int
     cdef public list children
     cdef str _signature
+    cdef public SignatureType _child_0
+    cdef public SignatureType _child_1
 
 
 cdef class SignatureTree:

src/dbus_fast/signature.py

@@ -21,13 +21,22 @@ class SignatureType:
     """
 
     _tokens = "ybnqiuxtdsogavh({"
-    __slots__ = ("_signature", "children", "token", "token_as_int")
+    __slots__ = (
+        "_child_0",
+        "_child_1",
+        "_signature",
+        "children",
+        "token",
+        "token_as_int",
+    )
 
     def __init__(self, token: str) -> None:
         """Init a new SignatureType."""
         self.token: str = token
         self.token_as_int = ord(token)
         self.children: list[SignatureType] = []
+        self._child_0: Optional[SignatureType] = None
+        self._child_1: Optional[SignatureType] = None
         self._signature: Optional[str] = None
 
     def __eq__(self, other: object) -> bool:
@@ -60,6 +69,18 @@ class SignatureType:
         self._signature = self._collapse()
         return self._signature
 
+    def _add_child(self, child: "SignatureType") -> None:
+        """Add a child type to this type.
+
+        :param child: The child type to add.
+        :type child: :class:`SignatureType`
+        """
+        if self._child_0 is None:
+            self._child_0 = child
+        elif self._child_1 is None:
+            self._child_1 = child
+        self.children.append(child)
+
     @staticmethod
     def _parse_next(signature: str) -> tuple["SignatureType", str]:
         if not signature:
@@ -76,7 +97,7 @@ class SignatureType:
             (child, signature) = SignatureType._parse_next(signature[1:])
             if not child:
                 raise InvalidSignatureError("missing type for array")
-            self.children.append(child)
+            self._add_child(child)
             return (self, signature)
         if token == "(":
             self = SignatureType("(")
@@ -85,7 +106,7 @@ class SignatureType:
                 (child, signature) = SignatureType._parse_next(signature)
                 if not signature:
                     raise InvalidSignatureError('missing closing ")" for struct')
-                self.children.append(child)
+                self._add_child(child)
                 if signature[0] == ")":
                     return (self, signature[1:])
         elif token == "{":
@@ -94,13 +115,13 @@ class SignatureType:
             (key_child, signature) = SignatureType._parse_next(signature)
             if not key_child or len(key_child.children):
                 raise InvalidSignatureError("expected a simple type for dict entry key")
-            self.children.append(key_child)
+            self._add_child(key_child)
             (value_child, signature) = SignatureType._parse_next(signature)
             if not value_child:
                 raise InvalidSignatureError("expected a value for dict entry")
             if not signature or signature[0] != "}":
                 raise InvalidSignatureError('missing closing "}" for dict entry')
-            self.children.append(value_child)
+            self._add_child(value_child)
             return (self, signature[1:])
 
         # basic type

tests/test_signature.py

@@ -23,6 +23,15 @@ def test_multiple_simple():
         assert_simple_type("s", tree.types[i])
 
 
+def test_children():
+    tree = SignatureTree("ss")
+    assert len(tree.types) == 2
+    parent = tree.types[0]
+    assert parent.token == "s"
+    assert parent.signature == "s"
+    assert len(parent.children) == 0
+
+
 def test_array():
     tree = SignatureTree("as")
     assert len(tree.types) == 1
@@ -31,6 +40,11 @@ def test_array():
     assert child.token == "a"
     assert len(child.children) == 1
     assert_simple_type("s", child.children[0])
+    assert child.children[0].token == "s"
+    assert child._child_0.signature == "s"
+    assert child._child_1 is None
+    with pytest.raises(AttributeError):
+        _ = child._child_1.signature
 
 
 def test_array_multiple():
@@ -67,6 +81,8 @@ def test_simple_struct():
     assert len(child.children) == 3
     for i in range(3):
         assert_simple_type("s", child.children[i])
+    assert child._child_0.signature == "s"
+    assert child._child_1.signature == "s"
 
 
 def test_nested_struct():