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docs: Port GObject concepts to use G_DECLARE_FINAL_TYPE

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And G_DECLARE_INTERFACE.

https://bugzilla.gnome.org/show_bug.cgi?id=744060
This commit is contained in:
Philip Withnall 2015-02-23 15:32:47 +00:00
parent ab9b52e69c
commit e57741791e
1 changed files with 85 additions and 87 deletions
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172
docs/reference/gobject/tut_gtype.xml
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@ -225,57 +225,66 @@ static void test_object (void)
returns the GType for the associated object type. For an object of type
<emphasis>Bar</emphasis> in a library prefixed by <emphasis>maman</emphasis>,
use: <function>MAMAN_TYPE_BAR</function>.
It is common although not a convention to implement this macro using either a global
static variable or a function named <function>prefix_object_get_type</function>.
We will follow the function pattern wherever possible in this document.
</para></listitem>
<listitem><para>Create a macro named <function>PREFIX_OBJECT (obj)</function> which
returns a pointer of type <type>PrefixObject</type>. This macro is used to enforce
static type safety by doing explicit casts wherever needed. It also enforces
dynamic type safety by doing runtime checks. It is possible to disable the dynamic
type checks in production builds (see <link linkend="glib-building">building glib</link>).
For example, we would create
<function>MAMAN_BAR (obj)</function> to keep the previous example.
</para></listitem>
<listitem><para>If the type is classed, create a macro named
<function>PREFIX_OBJECT_CLASS (klass)</function>. This macro
is strictly equivalent to the previous casting macro: it does static casting with
dynamic type checking of class structures. It is expected to return a pointer
to a class structure of type <type>PrefixObjectClass</type>. Again, an example is:
<function>MAMAN_BAR_CLASS</function>.
</para></listitem>
<listitem><para>Create a macro named <function>PREFIX_IS_BAR (obj)</function>: this macro is expected
to return a <type>gboolean</type> which indicates whether or not the input
object instance pointer of type BAR.
</para></listitem>
<listitem><para>If the type is classed, create a macro named
<function>PREFIX_IS_OBJECT_CLASS (klass)</function> which, as above, returns a boolean
if the input class pointer is a pointer to a class of type OBJECT.
</para></listitem>
<listitem><para>If the type is classed, create a macro named
<function>PREFIX_OBJECT_GET_CLASS (obj)</function>
which returns the class pointer associated to an instance of a given type. This macro
is used for static and dynamic type safety purposes (just like the previous casting
macros).
This macro is implemented using a function named
<function>prefix_object_get_type</function>.
</para></listitem>
<listitem>
<para>
Use <link linkend="G-DECLARE-FINAL-TYPE:CAPS"><function>G_DECLARE_FINAL_TYPE</function></link>
or <link linkend="G-DECLARE-DERIVABLE-TYPE:CAPS"><function>G_DECLARE_DERIVABLE_TYPE</function></link>
to define various other conventional macros for your object:
</para>
<itemizedlist>
<listitem><para><function>PREFIX_OBJECT (obj)</function>, which
returns a pointer of type <type>PrefixObject</type>. This macro is used to enforce
static type safety by doing explicit casts wherever needed. It also enforces
dynamic type safety by doing runtime checks. It is possible to disable the dynamic
type checks in production builds (see <link linkend="glib-building">building GLib</link>).
For example, we would create
<function>MAMAN_BAR (obj)</function> to keep the previous example.
</para></listitem>
<listitem><para><function>PREFIX_OBJECT_CLASS (klass)</function>, which
is strictly equivalent to the previous casting macro: it does static casting with
dynamic type checking of class structures. It is expected to return a pointer
to a class structure of type <type>PrefixObjectClass</type>. An example is:
<function>MAMAN_BAR_CLASS</function>.
</para></listitem>
<listitem><para><function>PREFIX_IS_BAR (obj)</function>, which
returns a <type>gboolean</type> which indicates whether the input
object instance pointer is non-<type>NULL</type> and of type BAR.
</para></listitem>
<listitem><para><function>PREFIX_IS_OBJECT_CLASS (klass)</function>, which returns a boolean
if the input class pointer is a pointer to a class of type OBJECT.
</para></listitem>
<listitem><para><function>PREFIX_OBJECT_GET_CLASS (obj)</function>,
which returns the class pointer associated to an instance of a given type. This macro
is used for static and dynamic type safety purposes (just like the previous casting
macros).
</para></listitem>
</itemizedlist>
</listitem>
</itemizedlist>
The implementation of these macros is pretty straightforward: a number of simple-to-use
macros are provided in <filename>gtype.h</filename>. For the example we used above, we would
write the following trivial code to declare the macros:
<informalexample><programlisting>
#define MAMAN_TYPE_BAR (maman_bar_get_type ())
#define MAMAN_BAR(obj) (G_TYPE_CHECK_INSTANCE_CAST ((obj), MAMAN_TYPE_BAR, MamanBar))
#define MAMAN_BAR_CLASS(klass) (G_TYPE_CHECK_CLASS_CAST ((klass), MAMAN_TYPE_BAR, MamanBarClass))
#define MAMAN_IS_BAR(obj) (G_TYPE_CHECK_INSTANCE_TYPE ((obj), MAMAN_TYPE_BAR))
#define MAMAN_IS_BAR_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), MAMAN_TYPE_BAR))
#define MAMAN_BAR_GET_CLASS(obj) (G_TYPE_INSTANCE_GET_CLASS ((obj), MAMAN_TYPE_BAR, MamanBarClass))
#define MAMAN_TYPE_BAR maman_bar_get_type ()
G_DECLARE_FINAL_TYPE (MamanBar, maman_bar, MAMAN, BAR, GObject)
</programlisting></informalexample>
<note><simpara>Stick to the naming <varname>klass</varname> as <varname>class</varname> is a registered c++ keyword.</simpara></note>
</para>
<para>
The following code shows how to implement the <function>maman_bar_get_type</function>
function:
Unless your code has special requirements, you can use the
<function><link linkend="G-DEFINE-TYPE:CAPS">G_DEFINE_TYPE</link></function>
macro to define a class:
<informalexample><programlisting>
G_DEFINE_TYPE (MamanBar, maman_bar, G_TYPE_OBJECT)
</programlisting></informalexample>
</para>
<para>
Otherwise, the <function>maman_bar_get_type</function> function must be
implemented manually:
<informalexample><programlisting>
GType maman_bar_get_type (void)
{
@ -293,15 +302,6 @@ GType maman_bar_get_type (void)
</programlisting></informalexample>
</para>
<para>
If you have no special requirements you can use the
<function><link linkend="G-DEFINE-TYPE:CAPS">G_DEFINE_TYPE</link></function>
macro to define a class:
<informalexample><programlisting>
G_DEFINE_TYPE (MamanBar, maman_bar, G_TYPE_OBJECT)
</programlisting></informalexample>
</para>
</sect1>
<sect1 id="gtype-non-instantiable">
@ -650,13 +650,8 @@ B *b;
classed type which derives from
<link linkend="GTypeInterface"><type>GTypeInterface</type></link>. The following piece of code declares such an interface.
<informalexample><programlisting>
#define MAMAN_TYPE_IBAZ (maman_ibaz_get_type ())
#define MAMAN_IBAZ(obj) (G_TYPE_CHECK_INSTANCE_CAST ((obj), MAMAN_TYPE_IBAZ, MamanIbaz))
#define MAMAN_IS_IBAZ(obj) (G_TYPE_CHECK_INSTANCE_TYPE ((obj), MAMAN_TYPE_IBAZ))
#define MAMAN_IBAZ_GET_INTERFACE(inst) (G_TYPE_INSTANCE_GET_INTERFACE ((inst), MAMAN_TYPE_IBAZ, MamanIbazInterface))
typedef struct _MamanIbaz MamanIbaz; /* dummy object */
typedef struct _MamanIbazInterface MamanIbazInterface;
#define MAMAN_TYPE_IBAZ maman_ibaz_get_type ()
G_DECLARE_INTERFACE(MamanIbaz, maman_ibaz, MAMAN, IBAZ, GObject)
struct _MamanIbazInterface {
GTypeInterface parent;
@ -664,8 +659,6 @@ struct _MamanIbazInterface {
void (*do_action) (MamanIbaz *self);
};
GType maman_ibaz_get_type (void);
void maman_ibaz_do_action (MamanIbaz *self);
</programlisting></informalexample>
The interface function, <function>maman_ibaz_do_action</function> is implemented
@ -673,6 +666,8 @@ void maman_ibaz_do_action (MamanIbaz *self);
<informalexample><programlisting>
void maman_ibaz_do_action (MamanIbaz *self)
{
g_return_if_fail (MAMAN_IS_IBAZ (self));
MAMAN_IBAZ_GET_INTERFACE (self)->do_action (self);
}
</programlisting></informalexample>
@ -691,12 +686,38 @@ void maman_ibaz_do_action (MamanIbaz *self)
</para>
<para>
Once an interface type is registered, you must register implementations for these
interfaces. The function named <function>maman_baz_get_type</function> registers
a new GType named MamanBaz which inherits from <link linkend="GObject"><type>GObject</type></link> and which
implements the interface <type>MamanIbaz</type>.
If you have no special requirements you can use the
<link linkend="G-IMPLEMENT-INTERFACE:CAPS">G_IMPLEMENT_INTERFACE</link> macro
to implement an interface:
<informalexample><programlisting>
static void maman_baz_do_action (MamanIbaz *self)
static void
maman_baz_do_action (MamanIbaz *self)
{
g_print ("Baz implementation of Ibaz interface Action.\n");
}
static void
maman_ibaz_interface_init (MamanIbazInterface *iface)
{
iface->do_action = maman_baz_do_action;
}
G_DEFINE_TYPE_WITH_CODE (MamanBaz, maman_baz, G_TYPE_OBJECT,
G_IMPLEMENT_INTERFACE (MAMAN_TYPE_IBAZ,
maman_ibaz_interface_init));
</programlisting></informalexample>
</para>
<para>
If your code does have special requirements, you must write a custom
<function>get_type</function> function to register your GType which
inherits from some <link linkend="GObject"><type>GObject</type></link>
and which implements the interface <type>MamanIbaz</type>. For
example, this code registers a new <type>MamanBaz</type> class which
implements <type>MamanIbaz</type>:
<informalexample><programlisting>
static void
maman_baz_do_action (MamanIbaz *self)
{
g_print ("Baz implementation of Ibaz interface Action.\n");
}
@ -759,29 +780,6 @@ struct _GInterfaceInfo
</programlisting></informalexample>
</para>
<para>
If you have no special requirements you can use the
<link linkend="G-IMPLEMENT-INTERFACE:CAPS">G_IMPLEMENT_INTERFACE</link> macro
to implement an interface:
<informalexample><programlisting>
static void
maman_baz_do_action (MamanIbaz *self)
{
g_print ("Baz implementation of Ibaz interface Action.\n");
}
static void
maman_ibaz_interface_init (MamanIbazInterface *iface)
{
iface->do_action = maman_baz_do_action;
}
G_DEFINE_TYPE_WITH_CODE (MamanBaz, maman_baz, G_TYPE_OBJECT,
G_IMPLEMENT_INTERFACE (MAMAN_TYPE_IBAZ,
maman_ibaz_interface_init));
</programlisting></informalexample>
</para>
<sect2 id="gtype-non-instantiable-classed-init">
<title>Interface Initialization</title>