Merge pull request #73 from edwood-grant/patch-1

Fixing incorrect enum information and add alternatives

Author: colinkiama

source/developer-guides/bindings/writing-a-vapi-manually/04-00-recognizing-vala-semantics-in-c-code/04-02-enums-and-flags.rst

@@ -64,4 +64,78 @@ There is also a common tendency to use combinable bit patterns. These are conver
        CREATE
    }
 
-In Vala, enums and flags may have member functions. In particular, ``strerr``-like functions are best converted to member functions. 
+Supersets
+---------
+
+If one set of enums or flags is a superset of another, but they are logically separate, You can create a different set of enums that refer to the same enum
+or defines.
+
+For example:
+
+.. code-block:: c
+
+   #define FOO_A 1
+   #define FOO_B 2
+   #define FOO_C 3
+   #define FOO_D 4
+   /* takes FOO_A or B only */
+   void do_something(int);
+   /* takes any FOO_ value */
+   void do_something_else(int);
+
+Can become this:
+
+.. code-block:: vala
+
+   [CCode (cname = "int", cprefix = "FOO_", has_type_id = false)]
+   public enum Foo { A, B }
+   [CCode (cname = "int", cprefix = "FOO_", has_type_id = false)]
+   public enum FooExtended { C, D }
+
+You can then cast one enum to another:
+
+.. code-block:: vala
+    
+   var foo_enum = (Foo) FooExtended.C;
+
+Member functions and constants
+------------------------------
+
+In Vala, enums and flags may have member functions and constants.
+In particular, ``strerr``-like functions are best converted to member functions. 
+
+Enum aliases and ``to_string()``
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The default function ``to_string()`` can cause problems if the enum has aliases (the C error ``duplicate case`` will trigger). So to solve this, 
+you can create additional constants after the enum has been declared to add the missing enum aliases.
+
+For example this enum:
+
+.. code-block:: c
+
+   typedef enum {
+       BAR_A,
+       BAR_B,
+       BAR_C,
+       BAR_D,
+       BAR_FIRST = BAR_A,
+       BAR_LAST = BAR_D,
+   } bar_e;
+
+Will become:
+
+.. code-block:: vala
+
+   [CCode (cname = "bar_e", cprefix = "BAR_", has_type_id = false)]
+   public enum Bar {
+       A,
+       B,
+       C;
+
+       [CCode (cname = "BAR_")]
+       public const Bar FIRST;
+
+       [CCode (cname = "BAR_")]
+       public const Bar LAST;
+   }