Scala sealed trait ability (mostly) in dataconf using dataclass

README.md

@@ -69,6 +69,42 @@ class Config:
 
 print(dataconf.load(conf, Config))
 # TestConf(test='pc.home', float=2.1, default='hello', list=['a', 'b'], nested=Nested(a='test'), nested_list=[Nested(a='test1')], duration=relativedelta(seconds=+2), default_factory={}, union=1)
+
+# Replicating pureconfig Scala sealed trait case class behavior
+# https://pureconfig.github.io/docs/overriding-behavior-for-sealed-families.html
+class InputType:
+    @dataclass(init=True, repr=True)
+    class StringImpl:
+        name: Text
+        age: Text
+
+        def test_method(self):
+            print(f"{self.name} is {self.age} years old.")
+
+    @dataclass(init=True, repr=True)
+    class IntImpl:
+        area_code: int
+        phone_num: Text
+
+        def test_method(self):
+            print(f"The area code for {self.phone_num} is {str(self.area_code)}")
+
+@dataclass
+class Base:
+    location: Text
+    input_source: Union[InputType.StringImpl, InputType.IntImpl]
+
+str_conf = """
+{
+    location: Europe
+    input_source {
+        name: Thailand
+        age: "12"
+    }
+}
+"""
+
+conf = dataconf.loads(str_conf, Base)
 ```
 
 ```python

dataconf/__init__.py

@@ -2,5 +2,6 @@
 from dataconf.utils import dumps
 from dataconf.utils import load
 from dataconf.utils import loads
+from dataconf.version import __version__
 
-__all__ = ["load", "loads", "dump", "dumps"]
+__all__ = ["load", "loads", "dump", "dumps", "__version__"]

dataconf/utils.py

@@ -113,6 +113,26 @@ def __parse(value: any, clazz, path):
     if clazz is ConfigTree:
         return __parse_type(value, clazz, path, isinstance(value, ConfigTree))
 
+    # Todo: this should be cleaner
+    #       iterates through class dict to check for subclasses
+    #       if subclasses are a dataclass parse values
+    #       the idea here is to replicate parsing of a sealed trait in Scala
+    #       when using pureconfig
+    child_failures = []
+    for child_clazz in sorted(clazz.__subclasses__(), key=lambda c: c.__name__):
+        if is_dataclass(child_clazz):
+            try:
+                return __parse(value, child_clazz, path)
+            except TypeConfigException as f:
+                child_failures.append(str(f))
+
+    # no need to check length; false if empty
+    if child_failures:
+        fails = "\n- ".join(child_failures)
+        raise TypeConfigException(
+            f"expected type {clazz} at {path}, failed subclasses:{fails}"
+        )
+
     raise TypeConfigException(f"expected type {clazz} at {path}, got {type(value)}")
 
 

dataconf/version.py

@@ -0,0 +1,3 @@
+import importlib.metadata
+
+__version__ = importlib.metadata.version("dataconf")

pyproject.toml

@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "dataconf"
-version = "0.1.5"
+version = "0.1.6"
 description = "Lightweight configuration with automatic dataclasses parsing (HOCON/JSON/YAML/PROPERTIES)"
 authors = []
 license = "Apache2"

tests/scala_sealed_trait.py

@@ -0,0 +1,30 @@
+from dataclasses import dataclass
+from typing import Text
+
+
+class InputType:
+    pass
+
+
+@dataclass(init=True, repr=True)
+class StringImpl(InputType):
+    name: Text
+    age: Text
+
+    def test_method(self):
+        return f"{self.name} is {self.age} years old."
+
+    def test_complex(self):
+        return int(self.age) * 3
+
+
+@dataclass(init=True, repr=True)
+class IntImpl(InputType):
+    area_code: int
+    phone_num: Text
+
+    def test_method(self):
+        return f"The area code for {self.phone_num} is {str(self.area_code)}"
+
+    def test_complex(self):
+        return self.area_code - 10

tests/test_parser.py

@@ -13,6 +13,9 @@
 from dataconf.exceptions import UnexpectedKeysException
 from dateutil.relativedelta import relativedelta
 import pytest
+from tests.scala_sealed_trait import InputType
+from tests.scala_sealed_trait import IntImpl
+from tests.scala_sealed_trait import StringImpl
 
 
 PARENT_DIR = os.path.normpath(
@@ -241,3 +244,51 @@ class Base:
             production=True,
             conn=Conn(host="test.server.io", port=443),
         )
+
+    def test_traits_string_impl(self) -> None:
+        @dataclass
+        class Base:
+            location: Text
+            input_source: InputType
+
+        str_conf = """
+        {
+            location: Europe
+            input_source {
+                name: Thailand
+                age: "12"
+            }
+        }
+        """
+
+        conf = loads(str_conf, Base)
+        assert conf == Base(
+            location="Europe",
+            input_source=StringImpl(name="Thailand", age="12"),
+        )
+        assert conf.input_source.test_method() == "Thailand is 12 years old."
+        assert conf.input_source.test_complex() == 36
+
+    def test_traits_int_impl(self) -> None:
+        @dataclass
+        class Base:
+            location: Text
+            input_source: InputType
+
+        str_conf = """
+        {
+            location: Europe
+            input_source {
+                area_code: 94
+                phone_num: "1234567"
+            }
+        }
+        """
+
+        conf = loads(str_conf, Base)
+        assert conf == Base(
+            location="Europe",
+            input_source=IntImpl(area_code=94, phone_num="1234567"),
+        )
+        assert conf.input_source.test_method() == "The area code for 1234567 is 94"
+        assert conf.input_source.test_complex() == 84