add description

src/class/typeob.rs

@@ -10,25 +10,23 @@ use callback::AbortOnDrop;
 use class::{BaseObject, PyMethodDefType};
 
 
-/// Trait implemented by Python object types that have a corresponding type object.
-pub trait PyTypeObject {
-
-    /// Retrieves the type object for this Python object type.
-    fn type_object(py: Python) -> PyType;
-
-}
-
-
-/// Trait implemented by object that generated by py::class macro
+/// Basic python type information
+/// Implementing this trait for custom struct is enough to make it compatible with
+/// python object system
 pub trait PyTypeInfo {
+    /// Type of objects to store in PyObject struct
     type Type;
 
+    /// Size of the PyObject structure
     fn size() -> usize;
 
+    /// `Type` instance offset inside PyObject structure
     fn offset() -> isize;
 
+    /// Type name
     fn type_name() -> &'static str;
 
+    /// PyTypeObject instance for this type
     fn type_object() -> &'static mut ffi::PyTypeObject;
 
 }
@@ -84,6 +82,14 @@ impl<'a, T> PyTypeInfo for Py<'a, T> where T: PyTypeInfo {
 }
 
 
+/// Trait implemented by Python object types that have a corresponding type object.
+pub trait PyTypeObject {
+
+    /// Retrieves the type object for this Python object type.
+    fn type_object(py: Python) -> PyType;
+
+}
+
 impl<T> PyTypeObject for T where T: BaseObject + PyTypeInfo {
 
     #[inline]