Update object.md

docs/object.md

@@ -5,3 +5,33 @@ Object is the root class of every object inside Gravity. Through the Object clas
 All the built-in Gravity type are built from the base Object class and when you declare a new Class in Gravity without a super class then it is set by default to Object.
 
 The new [Introspection](introspection.md) feature is built on top of the base Object class (so any other Class automatically inherits that feature).
+
+## Built-in types
+
+Gravity has some built-in types that extend and overrides methods and classes from the base Object class:
+* [Int](int.md)
+* [Float](float.md)
+* [String](string.md)
+* [Bool](bool.md)
+* [Null](null.md)
+* [Class](class.md)
+* [Function](func.md)
+* [Fiber](fiber.md)
+* Instance
+* [List](list.md)
+* [Map](map.md)
+* [Range](range.md)
+* [Function](func.md)
+* [Closure](closure.md)
+* [Fiber](fiber.md)
+
+## Special internal methods
+Some methods has a very special meaning, for example by implementing the **exec** method your class is able to be executable via the object() notation. By implementing the **loadat/storeat** method your object can be accessed via the subscript shortcut object[i]. The **load/store** method is internally used to implement the dot notation (object.property).
+
+The Class class overrides the exec method in order to implement Object instantiation and initialization:
+```swift
+  var foo = Foo()
+  // means execute the exec method of the Foo class
+```
+
+All these special methods are implemented by the base Object class in order to provide most the basic functionalities that an user expects for a modern object oriented programming language.