Expand the build_prefab function

src/ducktools/classbuilder/__init__.py

@@ -21,7 +21,7 @@
 # SOFTWARE.
 import sys
 
-__version__ = "v0.5.0"
+__version__ = "v0.5.1"
 
 # Change this name if you make heavy modifications
 INTERNALS_DICT = "__classbuilder_internals__"
@@ -359,26 +359,49 @@ def from_field(cls, fld, /, **kwargs):
         return cls(**argument_dict)
 
 
+class GatheredFields:
+    __slots__ = ("fields", "modifications")
+
+    def __init__(self, fields, modifications):
+        self.fields = fields
+        self.modifications = modifications
+
+    def __call__(self, cls):
+        return self.fields, self.modifications
+
+
 # Use the builder to generate __repr__ and __eq__ methods
-# and pretend `Field` was a built class all along.
+# for both Field and GatheredFields
 _field_internal = {
     "default": Field(default=NOTHING),
     "default_factory": Field(default=NOTHING),
     "type": Field(default=NOTHING),
     "doc": Field(default=None),
 }
 
+_gathered_field_internal = {
+    "fields": Field(default=NOTHING),
+    "modifications": Field(default=NOTHING),
+}
+
 _field_methods = {repr_maker, eq_maker}
 if _UNDER_TESTING:
     _field_methods.update({frozen_setattr_maker, frozen_delattr_maker})
 
 builder(
     Field,
-    gatherer=lambda cls_: (_field_internal, {}),
+    gatherer=GatheredFields(_field_internal, {}),
     methods=_field_methods,
     flags={"slotted": True, "kw_only": True},
 )
 
+builder(
+    GatheredFields,
+    gatherer=GatheredFields(_gathered_field_internal, {}),
+    methods={repr_maker, eq_maker},
+    flags={"slotted": True, "kw_only": False},
+)
+
 
 # Slot gathering tools
 # Subclass of dict to be identifiable by isinstance checks
@@ -430,6 +453,13 @@ def field_slot_gatherer(cls):
         slot_replacement = {}
 
         for k, v in cls_slots.items():
+            # Special case __dict__ and __weakref__
+            # They should be included in the final `__slots__`
+            # But ignored as a value.
+            if k in {"__dict__", "__weakref__"}:
+                slot_replacement[k] = None
+                continue
+
             if isinstance(v, field_type):
                 attrib = v
                 if attrib.type is not NOTHING:

src/ducktools/classbuilder/__init__.pyi

@@ -92,6 +92,25 @@ class Field:
     def from_field(cls, fld: Field, /, **kwargs: typing.Any) -> Field: ...
 
 
+class GatheredFields:
+    __slots__ = ("fields", "modifications")
+
+    fields: dict[str, Field]
+    modifications: dict[str, typing.Any]
+
+    __classbuilder_internals__: dict
+
+    def __init__(
+        self,
+        fields: dict[str, Field],
+        modifications: dict[str, typing.Any]
+    ) -> None: ...
+
+    def __repr__(self) -> str: ...
+    def __eq__(self, other) -> bool: ...
+    def __call__(self, cls: type) -> tuple[dict[str, Field], dict[str, typing.Any]]: ...
+
+
 class SlotFields(dict):
     ...
 

src/ducktools/classbuilder/prefab.py

@@ -30,7 +30,7 @@
 
 from . import (
     INTERNALS_DICT, NOTHING,
-    Field, MethodMaker, SlotFields,
+    Field, MethodMaker, SlotFields, GatheredFields,
     builder, fieldclass, get_flags, get_fields, make_slot_gatherer,
     frozen_setattr_maker, frozen_delattr_maker, is_classvar,
 )
@@ -519,6 +519,7 @@ def _make_prefab(
     frozen=False,
     dict_method=False,
     recursive_repr=False,
+    gathered_fields=None,
 ):
     """
     Generate boilerplate code for dunder methods in a class.
@@ -535,6 +536,7 @@ def _make_prefab(
                    such as lists)
     :param dict_method: Include an as_dict method for faster dictionary creation
     :param recursive_repr: Safely handle repr in case of recursion
+    :param gathered_fields: Pre-gathered fields callable, to skip re-collecting attributes
     :return: class with __ methods defined
     """
     cls_dict = cls.__dict__
@@ -546,12 +548,16 @@ def _make_prefab(
         )
 
     slots = cls_dict.get("__slots__")
-    if isinstance(slots, SlotFields):
-        gatherer = slot_prefab_gatherer
-        slotted = True
+    if gathered_fields is None:
+        if isinstance(slots, SlotFields):
+            gatherer = slot_prefab_gatherer
+            slotted = True
+        else:
+            gatherer = attribute_gatherer
+            slotted = False
     else:
-        gatherer = attribute_gatherer
-        slotted = False
+        gatherer = gathered_fields
+        slotted = False if slots is None else True
 
     methods = set()
 
@@ -770,6 +776,7 @@ def build_prefab(
     frozen=False,
     dict_method=False,
     recursive_repr=False,
+    slots=False,
 ):
     """
     Dynamically construct a (dynamic) prefab.
@@ -790,12 +797,35 @@ def build_prefab(
                    (This does not prevent the modification of mutable attributes such as lists)
     :param dict_method: Include an as_dict method for faster dictionary creation
     :param recursive_repr: Safely handle repr in case of recursion
+    :param slots: Make the resulting class slotted
     :return: class with __ methods defined
     """
-    class_dict = {} if class_dict is None else class_dict
-    cls = type(class_name, bases, class_dict)
+    class_dict = {} if class_dict is None else class_dict.copy()
+
+    class_annotations = {}
+    class_slots = {}
+    fields = {}
+
     for name, attrib in attributes:
-        setattr(cls, name, attrib)
+        if isinstance(attrib, Attribute):
+            fields[name] = attrib
+        elif isinstance(attrib, Field):
+            fields[name] = Attribute.from_field(attrib)
+        else:
+            fields[name] = Attribute(default=attrib)
+
+        if attrib.type is not NOTHING:
+            class_annotations[name] = attrib.type
+
+        class_slots[name] = attrib.doc
+
+    if slots:
+        class_dict["__slots__"] = class_slots
+
+    class_dict["__annotations__"] = class_annotations
+    cls = type(class_name, bases, class_dict)
+
+    gathered_fields = GatheredFields(fields, {})
 
     cls = _make_prefab(
         cls,
@@ -808,6 +838,7 @@ def build_prefab(
         frozen=frozen,
         dict_method=dict_method,
         recursive_repr=recursive_repr,
+        gathered_fields=gathered_fields,
     )
 
     return cls

src/ducktools/classbuilder/prefab.pyi

@@ -109,6 +109,7 @@ def _make_prefab(
     frozen: bool = False,
     dict_method: bool = False,
     recursive_repr: bool = False,
+    gathered_fields: Callable[[type], tuple[dict[str, Attribute], dict[str, typing.Any]]] | None = None,
 ) -> type: ...
 
 _T = typing.TypeVar("_T")
@@ -146,6 +147,7 @@ def build_prefab(
     frozen: bool = False,
     dict_method: bool = False,
     recursive_repr: bool = False,
+    slots: bool = False,
 ) -> type: ...
 
 def is_prefab(o: typing.Any) -> bool: ...

tests/prefab/dynamic/test_construction.py

@@ -91,3 +91,25 @@ class KeywordPrefab:
         a: int = 0
         b: int = attribute(kw_only=True)
         c: int = attribute()  # kw_only should be ignored
+
+
+def test_build_slotted():
+    SlottedClass = build_prefab(
+        "SlottedClass",
+        [
+            ("x", attribute(doc="x co-ordinate", type=float)),
+            ("y", attribute(default=0, doc="y co-ordinate", type=float))
+        ],
+        slots=True,
+    )
+
+    inst = SlottedClass(1)
+    assert inst.x == 1
+    assert inst.y == 0
+    assert SlottedClass.__slots__ == {'x': "x co-ordinate", 'y': "y co-ordinate"}
+
+    assert SlottedClass.__annotations__ == {'x': float, 'y': float}
+
+    # Test slots are functioning
+    with pytest.raises(AttributeError):
+        inst.z = 0

tests/test_core.py

@@ -14,6 +14,7 @@
     slot_gatherer,
     slotclass,
     fieldclass,
+    GatheredFields,
 )
 
 
@@ -299,6 +300,58 @@ class SlotClass:
     assert "__eq__" not in SlotClass.__dict__
 
 
+def test_slotclass_weakref():
+    import weakref
+
+    @slotclass
+    class WeakrefClass:
+        __slots__ = SlotFields(
+            a=1,
+            b=2,
+            __weakref__=None,
+        )
+
+    flds = get_fields(WeakrefClass)
+    assert 'a' in flds
+    assert 'b' in flds
+    assert '__weakref__' not in flds
+
+    slots = WeakrefClass.__slots__
+    assert 'a' in slots
+    assert 'b' in slots
+    assert '__weakref__' in slots
+
+    # Test weakrefs can be created
+    inst = WeakrefClass()
+    ref = weakref.ref(inst)
+    assert ref == inst.__weakref__
+
+
+def test_slotclass_dict():
+    @slotclass
+    class DictClass:
+        __slots__ = SlotFields(
+            a=1,
+            b=2,
+            __dict__=None,
+        )
+
+    flds = get_fields(DictClass)
+    assert 'a' in flds
+    assert 'b' in flds
+    assert '__dict__' not in flds
+
+    slots = DictClass.__slots__
+    assert 'a' in slots
+    assert 'b' in slots
+    assert '__dict__' in slots
+
+    # Test if __dict__ is included new values can be added
+    inst = DictClass()
+    inst.c = 42
+    assert inst.__dict__ == {"c": 42}
+
+
 def test_fieldclass():
     @fieldclass
     class NewField(Field):
@@ -374,3 +427,31 @@ class SlotClass:
     assert x.a == 12
     assert x.b == 2
     assert x.c == []
+
+
+def test_gatheredfields():
+    fields = {"x": Field(default=1)}
+    modifications = {"x": NOTHING}
+
+    alt_fields = {"x": Field(default=1), "y": Field(default=2)}
+
+    flds = GatheredFields(fields, modifications)
+    flds_2 = GatheredFields(fields, modifications)
+    flds_3 = GatheredFields(alt_fields, modifications)
+
+    class Ex:
+        pass
+
+    assert flds(Ex) == (fields, modifications)
+
+    assert flds == flds_2
+    assert flds != flds_3
+    assert flds != object()
+
+    assert repr(flds).endswith(
+        "GatheredFields("
+        "fields={'x': Field(default=1, default_factory=<NOTHING OBJECT>, type=<NOTHING OBJECT>, doc=None)}, "
+        "modifications={'x': <NOTHING OBJECT>}"
+        ")"
+    )
+