Add heritage page (#121)

docs/guides/heritage.md

@@ -0,0 +1,21 @@
+# Extend galcheat objects
+
+## Frozen dataclasses
+
+The goal of galcheat is to provide a **sourced reference** for survey parameters. Therefore the `Survey` and `Filter` objects have been implemented as frozen dataclasses. This means that trying to modify the attributes of an instance of a `Survey` or a `Filter` will raise a `FrozenInstanceError`.
+
+Nevertheless, one might possibly want to modify or extend the instances of the dataclasses found in galcheat for specific purposes. This can be achieved through inheritance.
+
+## Inheritance
+
+A frozen dataclass creates a class for which the call to the `__setattr__` method raises a `FrozenInstanceError`. A short way to bypass that feature is to inherit from the main class and modify the `__setattr__` method to recover its classic behavior.
+
+```python
+class ExtensibleSurvey(Survey):
+     def __setattr__(self, x, val):
+         self.__dict__[x] = val
+```
+
+The `ExtensibleSurvey` will behave just as the galcheat `Survey` and will be extendable or modifiable. This is also true for the `Filter` class.
+
+!!! warning "To be used at you own risk"

mkdocs.yml

@@ -36,6 +36,7 @@ nav:
     - Parameters: parameters.md
   - Guides:
       - Getting Started: guides/getting-started.md
+      - Extend galcheat objects: guides/heritage.md
       - Releases: guides/releases.md
   - API:
       - galcheat.survey: api/survey.md