doc: add chapter for alternative projects

docs/mkdocs.yml

@@ -93,5 +93,6 @@ nav:
       - Performance & caching: other/performance-and-caching.md
       - Static analysis — PHPStan/Psalm: other/static-analysis.md
   - Project:
+      - Alternatives: project/alternatives.md
       - Changelog: project/changelog.md
       - Credits: project/credits.md

docs/pages/project/alternatives.md

@@ -0,0 +1,31 @@
+# Alternatives to this library
+
+Mapping and hydration have been available in the PHP world for a long time.
+This library aims to bring powerful features to this aspect, some of which are
+missing in similar packages:
+
+- Objects have a valid state when mapping is over.
+- Validation is recursively applied on the input during mapping, [reported 
+  error messages] bring clarity to missing or invalid values.  
+- Type declaration follow community standards developed by popular packages, 
+  meaning that [advanced types] like `list<string>`, `non-empty-string`, 
+  `positive-int`, `int<0, 42>`, shaped arrays, generic classes and more are 
+  handled and validated properly.
+- The mapper can be flexible, allowing for instance [type casting] when needed.
+- Mapped objects should not rely on inheritance.
+
+You may take a look at alternative projects, but some features listed above
+might be missing:
+
+- [`symfony/serializer`](https://github.com/symfony/serializer)
+- [`eventsauce/object-hydrator`](https://github.com/EventSaucePHP/ObjectHydrator)
+- [`crell/serde`](https://github.com/Crell/Serde)
+- [`spatie/laravel-data`](https://github.com/spatie/laravel-data)
+- [`jms/serializer`](https://github.com/schmittjoh/serializer)
+- [`netresearch/jsonmapper`](https://github.com/cweiske/jsonmapper)
+- [`json-mapper/json-mapper`](https://github.com/JsonMapper/JsonMapper)
+- [`brick/json-mapper`](https://github.com/brick/json-mapper)
+
+[reported error messages]: ../usage/validation-and-error-handling.md
+[advanced types]: ../usage/type-reference.md
+[type casting]: ../usage/type-strictness-and-flexibility.md#enabling-flexible-casting