[PATCH 2/4] qom: provide convenient macros for declaring and defining types

[Daniel P . Berrangé]

When creating new QOM types, there is a lot of boilerplate code that
must be repeated using a standard pattern. This is tedious to write
and liable to suffer from subtle inconsistencies. Thus it would
benefit from some simple automation.

QOM was loosely inspired by GLib's GObject, and indeed GObject suffers
from the same burden of boilerplate code, but has long provided a set of
macros to eliminate this burden in the source implementation. More
recently it has also provided a set of macros to eliminate this burden
in the header declaration.

In GLib there are the G_DECLARE_* and G_DEFINE_* family of macros
for the header declaration and source implementation respectively:

  https://developer.gnome.org/gobject/stable/chapter-gobject.html
  https://developer.gnome.org/gobject/stable/howto-gobject.html

This patch takes inspiration from GObject to provide the equivalent
functionality for QOM.

In the header file, instead of:

    typedef struct MyDevice MyDevice;
    typedef struct MyDeviceClass MyDeviceClass;

    G_DEFINE_AUTOPTR_CLEANUP_FUNC(MyDeviceClass, object_unref)

    #define MY_DEVICE_GET_CLASS(void *obj) \
            OBJECT_GET_CLASS(MyDeviceClass, obj, TYPE_MY_DEVICE)
    #define MY_DEVICE_CLASS(void *klass) \
            OBJECT_CLASS_CHECK(MyDeviceClass, klass, TYPE_MY_DEVICE)
    #define MY_DEVICE(void *obj)
            OBJECT_CHECK(MyDevice, obj, TYPE_MY_DEVICE)

    struct MyDeviceClass {
        DeviceClass parent_class;
    };

We now have

    OBJECT_DECLARE_SIMPLE_TYPE(MyDevice, my_device, MY_DEVICE, DEVICE)

In cases where the class needs some virtual methods, it can be left
to be implemented manually using

    OBJECT_DECLARE_TYPE(MyDevice, my_device, MY_DEVICE)

Note that these macros are including support for g_autoptr() for the
object types, which is something previously only supported for variables
declared as the base Object * type.

Meanwhile in the source file, instead of:

    static void my_device_finalize(Object *obj);
    static void my_device_class_init(ObjectClass *oc, void *data);
    static void my_device_init(Object *obj);

    static const TypeInfo my_device_info = {
        .parent = TYPE_DEVICE,
        .name = TYPE_MY_DEVICE,
        .instance_size = sizeof(MyDevice),
        .instance_init = my_device_init,
        .instance_finalize = my_device_finalize,
        .class_size = sizeof(MyDeviceClass),
        .class_init = my_device_class_init,
    };

    static void
    my_device_register_types(void)
    {
        type_register_static(&my_device_info);
    }
    type_init(my_device_register_types);

We now have

    OBJECT_DEFINE_TYPE(MyDevice, my_device, MY_DEVICE, DEVICE)

Or, if a class needs to implement interfaces:

    OBJECT_DEFINE_TYPE_WITH_INTERFACES(MyDevice, my_device, MY_DEVICE, DEVICE,
                                       { TYPE_USER_CREATABLE }, { NULL })

Or, if a class needs to be abstract

    OBJECT_DEFINE_ABSTRACT_TYPE(MyDevice, my_device, MY_DEVICE, DEVICE)

IOW, in both cases the maintainer now only has to think about the
interesting part of the code which implements useful functionality
and avoids much of the boilerplate.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 include/qom/object.h | 277 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 277 insertions(+)

diff --git a/include/qom/object.h b/include/qom/object.h
index 1f8aa2d48e..be64421089 100644
--- a/include/qom/object.h
+++ b/include/qom/object.h
@@ -304,6 +304,119 @@ typedef struct InterfaceInfo InterfaceInfo;
  *
  * The first example of such a QOM method was #CPUClass.reset,
  * another example is #DeviceClass.realize.
+ *
+ * # Standard type declaration and definition macros #
+ *
+ * A lot of the code outlined above follows a standard pattern and naming
+ * convention. To reduce the amount of boilerplate code that needs to be
+ * written for a new type there are two sets of macros to generate the
+ * common parts in a standard format.
+ *
+ * A type is declared using the OBJECT_DECLARE macro family. In types
+ * which do not require any virtual functions in the class, the
+ * OBJECT_DECLARE_SIMPLE_TYPE macro is suitable, and is commonly placed
+ * in the header file:
+ *
+ * <example>
+ *   <title>Declaring a simple type</title>
+ *   <programlisting>
+ *     OBJECT_DECLARE_SIMPLE_TYPE(MyDevice, my_device, MY_DEVICE, DEVICE)
+ *   </programlisting>
+ * </example>
+ *
+ * This is equivalent to the following:
+ *
+ * <example>
+ *   <title>Expansion from declaring a simple type</title>
+ *   <programlisting>
+ *     typedef struct MyDevice MyDevice;
+ *     typedef struct MyDeviceClass MyDeviceClass;
+ *
+ *     G_DEFINE_AUTOPTR_CLEANUP_FUNC(MyDeviceClass, object_unref)
+ *
+ *     #define MY_DEVICE_GET_CLASS(void *obj) \
+ *             OBJECT_GET_CLASS(MyDeviceClass, obj, TYPE_MY_DEVICE)
+ *     #define MY_DEVICE_CLASS(void *klass) \
+ *             OBJECT_CLASS_CHECK(MyDeviceClass, klass, TYPE_MY_DEVICE)
+ *     #define MY_DEVICE(void *obj)
+ *             OBJECT_CHECK(MyDevice, obj, TYPE_MY_DEVICE)
+ *
+ *     struct MyDeviceClass {
+ *         DeviceClass parent_class;
+ *     };
+ *   </programlisting>
+ * </example>
+ *
+ * The 'struct MyDevice' needs to be declared separately.
+ * If the type requires virtual functions to be declared in the class
+ * struct, then the alternative OBJECT_DECLARE_TYPE() macro can be
+ * used. This does the same as OBJECT_DECLARE_SIMPLE_TYPE(), but without
+ * the 'struct MyDeviceClass' definition.
+ *
+ * To implement the type, the OBJECT_DEFINE macro family is available.
+ * In the simple case the OBJECT_DEFINE_TYPE macro is suitable:
+ *
+ * <example>
+ *   <title>Defining a simple type</title>
+ *   <programlisting>
+ *     OBJECT_DEFINE_TYPE(MyDevice, my_device, MY_DEVICE, DEVICE)
+ *   </programlisting>
+ * </example>
+ *
+ * This is equivalent to the following:
+ *
+ * <example>
+ *   <title>Expansion from defining a simple type</title>
+ *   <programlisting>
+ *     static void my_device_finalize(Object *obj);
+ *     static void my_device_class_init(ObjectClass *oc, void *data);
+ *     static void my_device_init(Object *obj);
+ *
+ *     static const TypeInfo my_device_info = {
+ *         .parent = TYPE_DEVICE,
+ *         .name = TYPE_MY_DEVICE,
+ *         .instance_size = sizeof(MyDevice),
+ *         .instance_init = my_device_init,
+ *         .instance_finalize = my_device_finalize,
+ *         .class_size = sizeof(MyDeviceClass),
+ *         .class_init = my_device_class_init,
+ *     };
+ *
+ *     static void
+ *     my_device_register_types(void)
+ *     {
+ *         type_register_static(&my_device_info);
+ *     }
+ *     type_init(my_device_register_types);
+ *   </programlisting>
+ * </example>
+ *
+ * This is sufficient to get the type registered with the type
+ * system, and the three standard methods now need to be implemented
+ * along with any other logic required for the type.
+ *
+ * If the type needs to implement one or more interfaces, then the
+ * OBJECT_DEFINE_TYPE_WITH_INTERFACES() macro can be used instead.
+ * This accepts an array of interface type names.
+ *
+ * <example>
+ *   <title>Defining a simple type implementing interfaces</title>
+ *   <programlisting>
+ *     OBJECT_DEFINE_TYPE_WITH_INTERFACES(MyDevice, my_device,
+ *                                        MY_DEVICE, DEVICE,
+ *                                        { TYPE_USER_CREATABLE }, { NULL })
+ *   </programlisting>
+ * </example>
+ *
+ * If the type is not intended to be instantiated, then then
+ * the OBJECT_DEFINE_ABSTRACT_TYPE() macro can be used instead:
+ *
+ * <example>
+ *   <title>Defining a simple type</title>
+ *   <programlisting>
+ *     OBJECT_DEFINE_ABSTRACT_TYPE(MyDevice, my_device, MY_DEVICE, DEVICE)
+ *   </programlisting>
+ * </example>
  */
 
 
@@ -440,6 +553,170 @@ struct Object
     Object *parent;
 };
 
+/**
+ * OBJECT_DECLARE_TYPE:
+ * @ModuleObjName: the object name with initial capitalization
+ * @module_obj_name: the object name in lowercase with underscore separators
+ * @MODULE_OBJ_NAME: the object name in uppercase with underscore separators
+ *
+ * This macro is typically used in a header file, and will:
+ *
+ *   - create the typedefs for the object and class structs
+ *   - register the type for use with g_autoptr
+ *   - provide three standard type cast functions
+ *
+ * The object struct and class struct need to be declared manually.
+ */
+#define OBJECT_DECLARE_TYPE(ModuleObjName, module_obj_name, MODULE_OBJ_NAME) \
+    typedef struct ModuleObjName ModuleObjName; \
+    typedef struct ModuleObjName##Class ModuleObjName##Class; \
+    \
+    G_DEFINE_AUTOPTR_CLEANUP_FUNC(ModuleObjName##Class, object_unref) \
+    \
+    static inline G_GNUC_UNUSED ModuleObjName##Class * \
+    MODULE_OBJ_NAME##_GET_CLASS(void *obj) \
+    { return OBJECT_GET_CLASS(ModuleObjName##Class, obj, \
+                              TYPE_##MODULE_OBJ_NAME); } \
+    \
+    static inline G_GNUC_UNUSED ModuleObjName##Class * \
+    MODULE_OBJ_NAME##_CLASS(void *klass) \
+    { return OBJECT_CLASS_CHECK(ModuleObjName##Class, klass, \
+                                TYPE_##MODULE_OBJ_NAME); } \
+    \
+    static inline G_GNUC_UNUSED ModuleObjName * \
+    MODULE_OBJ_NAME(void *obj) \
+    { return OBJECT_CHECK(ModuleObjName, obj, \
+                          TYPE_##MODULE_OBJ_NAME); }
+
+/**
+ * OBJECT_DECLARE_SIMPLE_TYPE:
+ * @ModuleObjName: the object name with initial caps
+ * @module_obj_name: the object name in lowercase with underscore separators
+ * @MODULE_OBJ_NAME: the object name in uppercase with underscore separators
+ * @ParentModuleObjName: the parent object name with initial caps
+ *
+ * This does the same as OBJECT_DECLARE_TYPE(), but also declares
+ * the class struct, thus only the object struct needs to be declare
+ * manually.
+ *
+ * This macro should be used unless the class struct needs to have
+ * virtual methods declared.
+ */
+#define OBJECT_DECLARE_SIMPLE_TYPE(ModuleObjName, module_obj_name, \
+                                   MODULE_OBJ_NAME, ParentModuleObjName) \
+    OBJECT_DECLARE_TYPE(ModuleObjName, module_obj_name, MODULE_OBJ_NAME) \
+    struct ModuleObjName##Class { ParentModuleObjName##Class parent_class; };
+
+
+/**
+ * OBJECT_DEFINE_TYPE_EXTENDED:
+ * @ModuleObjName: the object name with initial caps
+ * @module_obj_name: the object name in lowercase with underscore separators
+ * @MODULE_OBJ_NAME: the object name in uppercase with underscore separators
+ * @PARENT_MODULE_OBJ_NAME: the parent object name in uppercase with underscore
+ *                          separators
+ * @ABSTRACT: boolean flag to indicate whether the object can be instantiated
+ * @...: list of initializers for "InterfaceInfo" to declare implemented 
interfaces
+ *
+ * This macro is typically used in a source file, and will:
+ *
+ *   - declare prototypes for _finalize, _class_init and _init methods
+ *   - declare the TypeInfo struct instance
+ *   - provide the constructor to register the type
+ *
+ * After using this macro, implementations of the _finalize, _class_init,
+ * and _init methods need to be written. Any of these can be zero-line
+ * no-op impls if no special logic is required for a given type.
+ *
+ * This macro should rarely be used, instead one of the more specialized
+ * macros is usually a better choice.
+ */
+#define OBJECT_DEFINE_TYPE_EXTENDED(ModuleObjName, module_obj_name, \
+                                    MODULE_OBJ_NAME, PARENT_MODULE_OBJ_NAME, \
+                                    ABSTRACT, ...) \
+    static void \
+    module_obj_name##_finalize(Object *obj); \
+    static void \
+    module_obj_name##_class_init(ObjectClass *oc, void *data); \
+    static void \
+    module_obj_name##_init(Object *obj); \
+    \
+    static const TypeInfo module_obj_name##_info = { \
+        .parent = TYPE_##PARENT_MODULE_OBJ_NAME, \
+        .name = TYPE_##MODULE_OBJ_NAME, \
+        .instance_size = sizeof(ModuleObjName), \
+        .instance_init = module_obj_name##_init, \
+        .instance_finalize = module_obj_name##_finalize, \
+        .class_size = sizeof(ModuleObjName##Class), \
+        .class_init = module_obj_name##_class_init, \
+        .abstract = ABSTRACT, \
+        .interfaces = (InterfaceInfo[]) { __VA_ARGS__ } , \
+    }; \
+    \
+    static void \
+    module_obj_name##_register_types(void) \
+    { \
+        type_register_static(&module_obj_name##_info); \
+    } \
+    type_init(module_obj_name##_register_types);
+
+/**
+ * OBJECT_DEFINE_TYPE:
+ * @ModuleObjName: the object name with initial caps
+ * @module_obj_name: the object name in lowercase with underscore separators
+ * @MODULE_OBJ_NAME: the object name in uppercase with underscore separators
+ * @PARENT_MODULE_OBJ_NAME: the parent object name in uppercase with underscore
+ *                          separators
+ *
+ * This is a specialization of OBJECT_DEFINE_TYPE_EXTENDED, which is suitable
+ * for the common case of a non-abstract type, without any interfaces.
+ */
+#define OBJECT_DEFINE_TYPE(ModuleObjName, module_obj_name, MODULE_OBJ_NAME, \
+                           PARENT_MODULE_OBJ_NAME) \
+    OBJECT_DEFINE_TYPE_EXTENDED(ModuleObjName, module_obj_name, \
+                                MODULE_OBJ_NAME, PARENT_MODULE_OBJ_NAME, \
+                                false, { NULL })
+
+/**
+ * OBJECT_DEFINE_TYPE_WITH_INTERFACES:
+ * @ModuleObjName: the object name with initial caps
+ * @module_obj_name: the object name in lowercase with underscore separators
+ * @MODULE_OBJ_NAME: the object name in uppercase with underscore separators
+ * @PARENT_MODULE_OBJ_NAME: the parent object name in uppercase with underscore
+ *                          separators
+ * @...: list of initializers for "InterfaceInfo" to declare implemented 
interfaces
+ *
+ * This is a specialization of OBJECT_DEFINE_TYPE_EXTENDED, which is suitable
+ * for the common case of a non-abstract type, with one or more implemented
+ * interfaces.
+ *
+ * Note when passing the list of interfaces, be sure to include the final
+ * NULL entry, e.g.  { TYPE_USER_CREATABLE }, { NULL }
+ */
+#define OBJECT_DEFINE_TYPE_WITH_INTERFACES(ModuleObjName, module_obj_name, \
+                                           MODULE_OBJ_NAME, \
+                                           PARENT_MODULE_OBJ_NAME, ...) \
+    OBJECT_DEFINE_TYPE_EXTENDED(ModuleObjName, module_obj_name, \
+                                MODULE_OBJ_NAME, PARENT_MODULE_OBJ_NAME, \
+                                false, __VA_ARGS__)
+
+/**
+ * OBJECT_DEFINE_ABSTRACT_TYPE:
+ * @ModuleObjName: the object name with initial caps
+ * @module_obj_name: the object name in lowercase with underscore separators
+ * @MODULE_OBJ_NAME: the object name in uppercase with underscore separators
+ * @PARENT_MODULE_OBJ_NAME: the parent object name in uppercase with underscore
+ *                          separators
+ *
+ * This is a specialization of OBJECT_DEFINE_TYPE_EXTENDED, which is suitable
+ * for defining an abstract type, without any interfaces.
+ */
+#define OBJECT_DEFINE_ABSTRACT_TYPE(ModuleObjName, module_obj_name, \
+                                    MODULE_OBJ_NAME, PARENT_MODULE_OBJ_NAME) \
+    OBJECT_DEFINE_TYPE_EXTENDED(ModuleObjName, module_obj_name, \
+                                MODULE_OBJ_NAME, PARENT_MODULE_OBJ_NAME, \
+                                true, { NULL })
+
 /**
  * TypeInfo:
  * @name: The name of the type.
-- 
2.26.2