core: add helper to 'freeze' dataclasses, in order to derive a schema from the properties

my/arbtt.py

@@ -67,7 +67,7 @@ class Entry:
 
 
 # todo multiple threads? not sure if would help much... (+ need to find offset somehow?)
-def entries() -> Iterable[Res[Entry]]:
+def entries() -> Iterable[Entry]:
     inps = list(inputs())
 
     base: List[PathIsh] = ['arbtt-dump', '--format=json']

my/core/cachew.py

@@ -1,11 +1,9 @@
+from .common import assert_subpackage; assert_subpackage(__name__)
+
 from contextlib import contextmanager
 from pathlib import Path
 from typing import Optional
 
-# can lead to some unexpected issues if you 'import cachew' which being in my/core directory.. so let's protect against it
-# NOTE: if we use overlay, name can be smth like my.origg.my.core.cachew ...
-assert 'my.core' in __name__, f'Expected module __name__ ({__name__}) to start with my.core'
-
 def disable_cachew() -> None:
     try:
         import cachew

my/core/common.py

@@ -556,3 +556,9 @@ def to_jsons(it) -> Iterable[Json]:
 
 datetime_naive = datetime
 datetime_aware = datetime
+
+
+def assert_subpackage(name: str) -> None:
+    # can lead to some unexpected issues if you 'import cachew' which being in my/core directory.. so let's protect against it
+    # NOTE: if we use overlay, name can be smth like my.origg.my.core.cachew ...
+    assert 'my.core' in name, f'Expected module __name__ ({name}) to start with my.core'

my/core/types.py

@@ -0,0 +1,71 @@
+from .common import assert_subpackage; assert_subpackage(__name__)
+
+import dataclasses as dcl
+import inspect
+from typing import TypeVar, Type
+
+D = TypeVar('D')
+
+
+def _freeze_dataclass(Orig: Type[D]):
+    ofields = [(f.name, f.type, f) for f in dcl.fields(Orig)]
+
+    # extract properties along with their types
+    props   = list(inspect.getmembers(Orig, lambda o: isinstance(o, property)))
+    pfields = [(name, inspect.signature(getattr(prop, 'fget')).return_annotation) for name, prop in props]
+    # FIXME not sure about name?
+    # NOTE: sadly passing bases=[Orig] won't work, python won't let us override properties with fields
+    RRR = dcl.make_dataclass('RRR', fields=[*ofields, *pfields])
+    # todo maybe even declare as slots?
+    return props, RRR
+
+
+# todo need some decorator thingie?
+from typing import Generic
+class Freezer(Generic[D]):
+    '''
+    Some magic which converts dataclass properties into fields.
+    It could be useful for better serialization, for performance, for using type as a schema.
+    For now only supports dataclasses.
+    '''
+
+    def __init__(self, Orig: Type[D]) -> None:
+        self.Orig = Orig
+        self.props, self.Frozen = _freeze_dataclass(Orig)
+
+    def freeze(self, value: D) -> D:
+        pvalues = {name: getattr(value, name) for name, _ in self.props}
+        return self.Frozen(**dcl.asdict(value), **pvalues)
+
+
+### tests
+
+def test_freezer() -> None:
+    from typing import Any
+    @dcl.dataclass
+    class A:
+        x: Any
+
+        # TODO what about error handling?
+        @property
+        def typed(self) -> int:
+            return self.x['an_int']
+
+        @property
+        def untyped(self):
+            return self.x['an_any']
+
+    val = A(x=dict(an_int=123, an_any=[1, 2, 3]))
+    af = Freezer(A)
+    fval = af.freeze(val)
+
+    fd = vars(fval)
+    assert fd['typed']   == 123
+    assert fd['untyped'] == [1, 2, 3]
+
+###
+
+# TODO shit. what to do with exceptions?
+#
+# TODO not entirely sure if best to use Frozen as the schema, or actually convert objects..
+# guess need to experiment and see

tests/core.py

@@ -16,3 +16,4 @@ from my.core.core_config    import *
 from my.core.error          import *
 from my.core.util           import *
 from my.core.discovery_pure import *
+from my.core.types          import *