GOB2(1)GOB2(1)NAME
GOB2 - The GObject Builder
SYNOPSISgob2 [ option ] ... file
DESCRIPTION
GObject Builder is a simple preprocessor for easily creating GObject
objects. It does not parse any C code and ignores any C errors. It is
in spirit similar to things like lex or yacc. In some ways it also
resembles java. But it is really just a simple preprocessor for creat‐
ing GObjects for use in C or C++ and it is not a programming language.
OPTIONS
-? -h --help
Display a simple help screen.
--version
Display version information
-w --exit-on-warn
Exit with an error code even when you encounter a warning.
--no-exit-on-warn
Exit with an error only on errors, not on warnings, this is the
default.
--for-cpp
Generate C++ code.
--no-extern-c
Never add the extern "C" to the header.
--no-gnu
Never generate any code with GNU C extensions. However all the
GNU C extensions are always wrapped in #ifdef __GNUC__, so code
using them compiles correctly even on non-GNU compilers. This
option is for purists only. (using GNU extensions some warnings
are eliminated, some ugly hacks and there is better argument
type safety, so it´s good to use them)
--no-touch
Don´t touch output files unless they really changed (implies
--no-touch-headers). Be careful with automake, see section PRE‐
VENTING SPURIOUS BUILDS.
--no-touch-headers
Don´t touch the generated header file unless it really changed,
this avoids spurious rebuilds, but can confuse some make systems
(automake in particular), so it is not enabled by default. Pri‐
vate header is still touched even if unchanged however.
--always-private-header
Always create a <basename>-private.h file, even if it would be
empty.
--ondemand-private-header
Create the private header only if it would have something in it,
that is, if there are some private data members or protected
methods. This is the default.
--no-private-header
Never create a private header file. If we use any private data
members, define the private data structure at the point in the
.c source where the class definition begins.
--m4 Preprocess source with m4. Following args will be passed to m4.
--m4-dir
Print directory that will be searched for m4 files.
-n --no-write
Do not write any output files, just check syntax of the input
file.
--no-lines
Do not print out the ´#line´ statements into the output. Useful
for debugging the auto-generated generated code.
--no-self-alias
Do not create the Self and SelfClass type aliases and the SELF,
IS_SELF and SELF_CLASS macros.
--no-kill-underscores
Do not remove the initial underscore from method names.
--always-private-struct
Always include the private pointer in the public header file.
This is useful for files which are part of a library and you
want to reserve the right to add some private data members with‐
out breaking binary compatibility.
-o --output-dir
The directory into which output should be placed.
--file-sep[=c]
Replace default `-´ file name separator. If no separator char‐
acter is given then none is used. Only one character can be
used.
TYPENAMES
Because we need to parse out different parts of the typename, sometimes
you need to specify the typename with some special syntax. Types are
specified in capitalized form and words are separated by `:´. The
first word of the type (which can be empty) is the "namespace". This
fact is for example used for the type checking macro and the type
macro. For "Gtk:New:Button", the macros will be GTK_IS_NEW_BUTTON and
GTK_TYPE_NEW_BUTTON. This colon separated format of typenames is used
in the class declaration header and for method argument types.
OUTPUT FILES
The filenames are created from the typename. The words are separated
by `-´ (this can be changed with --file-sep option) and all in lower
case. For example for an object named "Gtk:New:Button", the files are
gtk-new-button.c and gtk-new-button.h. If you are using C++ mode, the
output .c file will in fact be a .cc file. If you have any private
data members, a private header file will also be created, called <base‐
name>-private.h (for the example above it would be gtk-new-button-pri‐
vate.h). The public header file is created to be human readable and to
be used as a reference to the object. The .c source file is not cre‐
ated as a human readable source and is littered with #line statements,
which make the compiler attempt to point you to the right line in your
.gob file in case of parsing errors. The output should not be edited
by hand, and you should only edit the .gob file.
INCLUDING NORMAL C CODE IN THE OUTPUT FILES
To include some code directly in the output C file begin with ´%{´ on
an empty line and end the code with a ´%}´ on an empty line. These
sections will appear in the output files in the order they are given.
There are several other sections to which you can put code. You can
put it in the ´header´ section (which can be abbreviated ´h´) and it
will go into the public header file. You can also put it in the ´pri‐
vateheader´ section (abbreviated ´ph´) which will make the code go into
the private header file. Sometimes you want some code (other includes)
to appear before the extern "C" and the protecting define. To do this
you can put them into the ´headertop´ (or ´ht´) section. You may wish
to include code or comments in all the files, which you can do by
putting them into the ´all´ (or ´a´) section. Similarly, code you wish
to appear at the top of all files go in the ´alltop´ (or ´at´) section.
For example:
%alltop{
/* this will be on top of all output files */
%}
%headertop{
/* this will be on top of the public header */
%}
%privateheader{
/* this will go into the private header file */
%}
%h{
/* will be included in the header */
void somefunc(int i);
%}
%a{
/* will be included in all files */
%}
%{
/* will be included in the C file */
void somefunc(int i)
{
/* some code */
}
%}
INCLUDE FILES
Gob will automatically include the class header file at the top of the
.c source file. If you wish to include it somewhere else, put the
include into some %{ %} section above the class definition, and gob
will not include it automatically. This way you can avoid circular
includes and control where in the file do you want to include the
header.
If you made any data members private, gob will also create a source
file that will be called <basename>-private.h. Same rule as above
applies for this just as it does for the regular header file. If you
do explicitly include the regular header file, you should always
include this private header file below it. That is, if you use any
private data members. If you don´t, the private header file automati‐
cally includes the public header file, and thus the public header file
will be indirectly included at the very top of the file.
THE CLASS HEADER
There can be only one class per input file. Defining a class is sort
of like in Java, you define the class and write inline code directly
into the class definition. To define a class you need to specify the
new object name and the name of the object from which it is derived
from, such as this "class <new type> from <parent type> { <class code>
}". For example:
class Gtk:New:Button from Gtk:Button {
<class code>
}
To make an abstract class (to pass G_TYPE_FLAG_ABSTRACT) add
´(abstract)´ before the curly braces above. This works since version
2.0.13.
DATA MEMBERS
There are five types of data members. Three of them are normal data
members, one is class wide (global) in scope and one is a virtual one,
usually linked to a normal data member or a class wide data member.
The three normal data members are public, protected and private. Pub‐
lic and protected are basically just entries in the object structure,
while private has it´s own dynamically allocated private structure.
Protected members are always put after the public one in the structure
and are marked protected in the header file. There is only one identi‐
fier allowed per typename unlike in normal C. Example:
public int i;
private GtkWidget *h;
protected long k;
Public and protected data members are accessed normally as members of
the object struct. Example where ´i´ is as above a public data member:
object->i = 1;
The private data members are defined in a structure which is only
available inside the .c file, or by including a private header file.
You must access them using the structure _priv. Example where ´h´ is
the private data member (as in the above example):
object->_priv->h = NULL;
The _priv structure is defined in the <basename>-private.h. This file
is automatically included if you don´t include it yourself. You should
always explicitly include it in your .gob file if you explicitly also
include the main header file. The reason it is a separate header file
is that you can also include it in other places that need to access
this objects private data, such as if you have the majority of func‐
tionality of an object in a separate .c file. Or if a derived object
needs to access the protected methods.
In case you use the --no-private-header option, no private header file
is created and you can only access the _priv pointer below the class
definition in the .gob file.
Also note that this structure is dynamically allocated, and is freed in
the finalize handler. If you override the finalized handler, your code
will be run first and only then will the _priv structure be freed.
Classwide data members:
Sometimes you want a datamember to be shared by all objects. You then
need the "classwide" scope keyword. So for example the following adds
a global member foo:
classwide int foo;
To access the member you do the standard voodoo of getting the class
from the object and casting it to your class pointer. Thus the follow‐
ing would work:
SELF_CLASS(GTK_OBJECT(object)->klass)->foo = 20;
Automatic Initialization:
You can automatically initialize the public private and protected data
members without having to add an init method. The advantage here is
that initialization is kept close to the definition of the data member
and thus it´s easier to check. To do this, just add a ´=´ followed by
a number or a token. It is also possible to include arbitrary C code
for more elaborate initializations by putting it all in curly braces.
Note that the curly braces will not be printed into the output, but
since gob does not C parsing it needs them to figure out where the C
code ends. The code will be inserted into the init method, above the
user defined body. So for example the following will initialize an
integer to -1 and a string with a newly allocated string of "hello".
public int foo = -1;
private char *bar = {g_strdup("hello")};
Automatic Destruction:
Most data stored as pointers needs to have a function called when the
object is finalized to either free the data. Gob will let you define a
function to be called on the data the object is finalized. This is
achieved by putting ´destroywith´ followed by a function name after the
variable definition. It is only called if the data you defined this on
is not NULL, so you cans specify functions which do not handle NULL.
It is very much like the GDestroyNotify function used in GTK+ and glib
in many places. Unlike many other places, gob will not enforce any
kind of type safety here so be a little bit more careful. Any function
you give it will be called as a "void function(void *)". It will in
fact be cast into such a form before called. This is to avoid spurious
warnings for gtk calls to subclass methods. The function needs not be
of that form exactly, it just has to take one argument which is the
pointer to the data. You should also not define this on any non-
pointer data as the results may be undefined. Example:
public char *foo = {g_strdup("bar")}
destroywith g_free;
Note that the function name you give must be a real function and not
macro. Also note that this is always called in the "finalize" method
of GObject. It is always called after any user defined body of the
finalize handler.
Sometimes you may want to run arbitrary code on destruction. While
this can be perfectly well done in the finalize handler. Depending on
the style you may want to include all destruction/initialization code
together with the definition of the data member. Thus you may want to
put arbitrary code which will then be inserted into the "finalize"
method of GObject. This can be done with the "destroy" keyword fol‐
lowed by arbitrary code in curly braces. Inside this code a macro
called VAR will be define which refers to your variable. So for exam‐
ple destroying a GString can be either done with a helper routine or
the following code:
public GString *string = {g_string_new(NULL)}
destroy {
if(VAR) g_string_free(VAR, TRUE);
};
The thing to remember with these is that there are many ways to do this
and you´d better be consistent in your code in how you use the above
things. Also defining a helper routine that will do the destruction
will be a nicer thing to do if that´s a possibility. The "destroy"
keyword with code does take up more space in the file and it may become
more cluttered.
The data is zeroed out after being destroyed. This is to make debug‐
ging easier in case your code might try to access an already finalized
object. In case you have overridden the finalize method, your code
will be run first and only then will the destructors be called. You
should not however make any assumptions about the order at which the
destructors are called. If you have interdependencies between destruc‐
tors for different data members, you will have to do this in your own
finalize override function.
Automatic Unreffing:
This is very much like the automatic destruction, but is instead run in
the dispose method (it is among other places called from the "destroy"
method of GtkObject). All data and other objects that you need to
unref should be done here, and not at finalize time. The semantics are
otherwise the same as for the "destroywith" and "destroy" keywords,
except that you use "unrefwith" and "unref".
public G:Object *foo = NULL
unrefwith g_object_unref;
public G:Object *bar = NULL
unref {
g_object_unref (VAR);
};
GOBJECT PROPERTIES
The fourth type of a data member a property type. It is a named data
member which is one of the features of the GObject system. It just
defines a way to get and set some data, but you have to take care of
storing that data somewhere. So it is normal to also have a normal
private (or public) data member where you store the real data. You
normally need to define a get and a set handler. They are fragments of
C code that will be used to get the value or set the value of the argu‐
ment. Inside them you can use the define VAL to which you assign the
data or get the data. You should treat this VAL as a GValue which
stores the data of the correct type. You can also use the identifier
"self" as pointer to the object instance. The type is defined as one
of the GObject type enums, but without the G_TYPE_ prefix. There are
also some attributes of a property which you can set. For example the
following is a definition of an integer property ´height´ which will be
synchronized with a private integer data member also of the name
´height´.
private int height;
property INT height
(nick = _("Short nickname"),
blurb = _("Long description"),
minimum = 10,
maximum = 200,
default_value = 100)
set { self->_priv->height = g_value_get_int (VAL); }
get { g_value_set_int (VAL, self->_priv->height); };
The attributes are really optional though you should at least set some
of them. All property types have a ´nick´ and a ´blurb´ attribute and
you should set those accordingly. This will make runtime querying the
object nicer as things such as gui editors and class browsers can be
more verbose about the class itself. You can use the ´_("string")´
notation instead of just "string", and that will mark the string for
translation.
Almost all types also have a ´default_value´ attribute which sets the
initial value of this property (on object initialization, the set han‐
dler will be run automatically with this value). This value will be
overriden if the user sets a value of this property on the call to
g_object_new.
All the numeric types (including CHAR) have ´minimum´ and ´maximum´
attributes which can restrict the range. If you do not specify these
the range will be the full range that the data type can handle.
Types such as UNICHAR and BOOLEAN only have the ´nick´, ´blurb´ and
´default_value´ attributes.
The ENUM type has an ´enum_type´ attribute which is the exact type of
the enum. This is so that the property knows which exact type you can
set, rather then just knowing it is an enum. You should always create
an enum type specific for the enum itself (see section on the enum
types)
Similarly FLAGS type has a ´flags_type´ which again you should set to
the specific type of this flags data member.
There is a STRING type which has only the extra ´default_value´
attribute.
The OBJECT type is one of the types that doesn´t have a ´default_value´
and it only has an ´object_type´ attribute (in addition to nick and
blurb of course) that is the exact object type that this property
accepts. The object_type should be as a type, that is for example
´Gtk:Button´.
There is a BOXED type which is a pointer which has a boxed type defined
(such that GObject knows how to copy and destroy this pointer). Here
you will need to specify the ´boxed_type´ attribute with the specific
type of the boxed pointer.
There is also a POINTER type, which has only the ´nick´ and ´blurb´
attributes. This is for storing arbitrary pointers. You should be
careful with this one, as GObject knows nothing about the data stored
at this pointer. It is somewhat like a ´void *´ type.
There is also the PARAM type for storing parameters with a ´param_type´
attribute.
You should notice that this list is pretty much like the list of
g_param_spec_* functions from gobject/gparamspecs.h, and the attributes
are like the arguments of those functions. Note however that value
array is NOT supported yet.
You can also specify extra flags, such as CONSTRUCT or CONSTRUCT_ONLY
using the ´flags´ attribute. You can specify multiple flags by oring
them together with ´|´. These flags correspond to the GParamFlags enu‐
meration except do not include the G_PARAM_ prefix. So for example to
define an enumeration property, which is a CONSTRUCT_ONLY property, we
could do the following:
private SomeEnumerationType foo;
property ENUM foo
(nick = _("Short nickname"),
blurb = _("Long description"),
enum_type = Some:Enumeration:Type
default_value = SOME_ENUMERATION_VALUE,
flags = CONSTRUCT_ONLY,
link);
The above example also gives an example of automatic linking to a stan‐
dard data memember. By including the attribute ´link´ a get and set
handlers will be automatically added without having to type them by
hand. This is useful for a vast majority data types that are just
linked to some standard data member and do not need to do anything
extra on get or set.
Another extra feature of properties is the possibility of automatically
exporing methods to get and set the property. That is without having
to use g_object_set and g_object_get. This is achieved by adding an
´export´ attribute to the list of property attributes.
If you do not define a set or get handler, the property will automati‐
cally be only readable or writable as appropriate.
Gob2 also creates macros which can be used for type safe access to
properties through g_object_set and g_object_get. The macros are
called <type>_PROP_<argument name>(x) and <type>_GET_PROP_<argument
name>(x). They define both the string and the value part of the argu‐
ment. So for setting an argument of height, one would use (for object
type My:Object):
g_object_set (G_OBJECT (object),
MY_OBJECT_PROP_HEIGHT (7),
NULL);
And for getting, you would use:
int height;
g_object_get (G_OBJECT (object),
MY_OBJECT_GET_PROP_HEIGHT (&height),
NULL);
Note however that the type safety only works completely on GNU C com‐
pilers. The code will compile on other compilers but with minimal type
safety. For complete type safety it is useful to use the get/set meth‐
ods that are defined by using the ´export´ attribute.
To get bettery type safety on some of the property types, you can spec‐
ify the ´type´ attribute which will add casts where appropriate in code
dealing with this property. This is especially useful for POINTER and
OBJECT types. But even for others.
You can also override properties from parent objects (that is override
their implementation, not their attributes). Do this by adding the
special ´override´ attribute. For example if the parent object had a
´height´ property then you could override it by
private int height;
property INT height
(override)
set { self->_priv->height = g_value_get_int (VAL); }
get { g_value_set_int (VAL, self->_priv->height); };
Overriding is supported since gob 2.0.10.
METHODS
There is a whole array of possible methods. The three normal, "famil‐
iar" method types are private, protected and public. Public are
defined as normal functions with a prototype in the header file. Pro‐
tected methods are defined as normal methods (which you can call from
other files), but their prototype is placed in the private header file.
Private methods are defined as static functions with prototypes at the
top of the .c file. Then there are signal, virtual and override meth‐
ods. More on those later. You can also define init and class_init
methods with a special definition if you want to add code to the con‐
structors or you can just leave them out. You can also not define a
body for a method, by just using ´;´ instead of a body. This will
define an empty function. You can´t do this for non-void regular pub‐
lic, private or protected methods, however it is acceptable for non-
void virtual, signal and override methods.
Function argument lists:
For all but the init and class_init methods, you use the following syn‐
tax for arguments. The first argument can be just "self", which gob
will translate into a pointer to the object instance. The rest of the
arguments are very similar to normal C arguments. If the typename is
an object pointer you should use the syntax defined above with the
words separated by ´:´
<type> <argument id>
or
<type> <argument id> (check <list of checks>)
The checks are glib type preconditions, and can be the following:
"null", which tests pointers for being NULL, "type" which checks GTK+
object pointers for being the right type, "<test> <number>" which tests
numeric arguments for being a certain value. The test can be a
<,>,<=,>= != or ==. Example:
public int
foo (self,
int h (check > 0 < 11),
Gtk:Widget *w (check null type))
This will be the prototype of a function which has a self pointer as
the first argument, an integer argument which will be checked and has
to be more then 0 and less then 11, and a pointer to a GtkWidget object
instance and it is checked for being null and the type will also be
checked.
Error return:
Methods which have a return value, there also has to be something
returned if there is an error, such as if a precondition is not met.
The default is 0, casted to the type of the method. If you need to
return something else then you can specify an "onerror" keyword after
the prototype and after that a number, a token (an identifier) or a bit
of C code enclosed in braces {}. The braces will not be printed into
the output, they just delimit the string. For example:
public void * get_something (self, int i (check >= 0)) onerror NULL {
...
}
The onerror value is also used in overrides that have a return value,
in case there isn´t a parent method, PARENT_HANDLER will return it.
More about this later.
Default return:
Some signal and virtual methods have a return type. But what happens
if there is no default handler and no one connects to a signal. GOB2
will normally have the wrappers return whatever you specify with
onerror or ´0´ if you haven´t specified anything. You can also specify
a default return value with the keyword ´defreturn´. It´s use is iden‐
tical to the use of onerror, and you can in fact use both at the same
time. Example
virtual int get_some_int (self) onerror -1 defreturn 10 ;
That is an empty virtual method (in C++ terms a pure virtual). If you
never specify any handler for it in the derived children it will just
return 10.
Constructor methods:
There are two methods that handle the construction of an object, init
and class_init. You define them by just using the init or class_init
keyword with an untyped argument in the argument list. The argument
will be usable in your function as a pointer to your object or class
depending if it´s init or class_init. For example:
init (self) {
/* initialize the object here */
self->a = 9;
self->b = 9;
}
class_init (class) {
/* initialize the class, this is rarely needed */
class->blah = NULL;
}
The class_init function is very rarely needed as all standard class
initialization is taken care of for you by gob itself. The init func‐
tion should on the other hand be used whenever you need to construct or
initialize anything in the object to put it into a sane state.
Virtual methods:
Virtual methods are basically pointers in the class structure, so that
one can override the method in derived methods. That is to implement
the method in a derived class, you must then use an override method
(more on those later). They can be empty (if you put ´;´ instead of
the C code). A wrapper will also be defined which makes calling the
methods he same as public methods. This type of method is just a lit‐
tle bit "slower" then normal functions, but not as slow as signals.
You define them by using "virtual" keyword before the prototype. If
you put the keyword "private" right after the "virtual" keyword, the
wrapper will not be a public method, but a private one. You can do the
same with "protected" to make a protected wrapper.
Signals:
Signals are methods to which the user can bind other handlers and over‐
ride the default handler. The default handler is basically the method
body. This is the most versatile and flexible type of a method and
also the slowest. You need to specify a whole bunch of things when you
define a signal. One thing is when the default handler will be run,
first or last. You specify that by "first" or "last" right after the
"signal" keyword. Then you need to define the GObject enum types
(again without the G_TYPE_ prefix). For that you define the return
types and the types of arguments after the "self" pointer (not includ‐
ing the "self" pointer). You put it in the following syntax "<return
type> (<list of arguments>)". If the return type is void, the type
should be "NONE", the same should be for the argument list. The rest
of the prototype is the same as for other method types. The body can
also be empty, and also there is a public method wrapper which you can
use for calling the signal just like a public method. Example:
signal first INT (POINTER, INT)
int do_something (self, Gtk:Widget *w (check null type), int length)
{
...
}
or
signal last NONE (NONE) void foo (self);
If you don´t want the wrapper that emits the signal to be public, you
can include the keyword "private" after the "signal" keyword. This
will make the wrapper a normal private method. You can also make a
protected wrapper by using "protected" instead of "private".
If you don´t define a "first" or a "last", the default will be taken as
"last".
You can also add additional flags. You do this just like with the
argument flags, although this is probably very rare. These are the
G_SIGNAL_* flags, and you can add them without the G_SIGNAL_ prefix
into a parenthesis, just after the "signal" keyword. By default all
public signals are G_SIGNAL_ACTION.
Also gob2 creates a wrapper macros for typesafe signal connection.
That is you will be warned by the compiler if you pass a callback that
is not the correct prototype. This will again only warn you on gcc,
but it will compile without warning on another compiler. So as with
all the typesafety hacks in gob, it is better to test your objects
under gcc to get any warnings even if you are using a different com‐
piler in the end.
The methods that are created for you are:
<class_name>_connect__<signal_name> (<object>, <callback>, <data>)
<class_name>_connect_after__<signal_name> (<object>, <callback>, <data>)
<class_name>_connect_data__<signal_name> (<object>, <callback>, <data>,
<destroy_notify>, <flags>)
These three functions correspond to the g_signal_connect, g_signal_con‐
nect_after and g_signal_connect_data functions that you would normally
use, except they are for a specific signal. Also do note the two
underscores between the method name and the signal name. For example
to connect the signal "foo" on the object "Test:Object" you would do:
test_object_connect__foo (object, callback, data);
To use BOXED in the signal arguments you need to tell gob which type of
boxed argument you want to use. For this you can just add
BOXED_GTK_TYPE_STRING instead of BOXED. For example
BOXED_GTK_TYPE_TREE_ITER for GtkTreeIter. This works since version
2.0.13.
Override methods:
If you need to override some method (a signal or a virtual method of
some class in the parent tree of the new object), you can define and
override method. After the "override" keyword, you should put the
typename of the class you are overriding a method from. Other then
that it is the same as for other methods. The "self" pointer in this
case should be the type of the method you are overriding so that you
don´t get warnings during compilation. Also to call the method of the
parent class, you can use the PARENT_HANDLER macro with your arguments.
Example:
override (Gtk:Container) void
add (Gtk:Container *self (check null type), Gtk:Widget *wid (check null type))
{
/* some code here */
PARENT_HANDLER(self, wid);
}
If the function has a return value, then PARENT_HANDLER is an expres‐
sion that you can use. It will return whatever the parent handler
returned, or the "onerror" expression if there was no parent handler.
Method names:
Inside the code, aliases are set for the methods, so that you don´t
have to type the class name before each call, just type self_ instead
of the name of the class. So to call a method called blah, you would
use the name self_blah. Example:
private int
foo (self)
{
return self->len;
}
private int
bar (self, int i)
{
return self_foo (self) + i;
}
MAKING NEW OBJECTS
You should define a new method which should be a normal public method.
Inside this method, you can use the GET_NEW macro that is defined for
you and that will fetch a new object, so a fairly standard new method
would look like:
public GObject *
new (void) {
GObject *ret = GET_NEW;
return G_OBJECT (ret);
}
You should not a subtle peculiarity of the GObject system here. If
there is any code inside the G_OBJECT macro argument, it will get exe‐
cuted multiple times. This means that things such as G_OBJECT(GET_NEW)
would actually create 4 objects, leaking 3 of them. A good rule (as
with anywhere in C) is to be careful with all macros.
SELF REFERENCES
Self alias casts:
There are some standard casts defined for you. Instead of using the
full macros inside the .c file, you can use SELF, IS_SELF and
SELF_CLASS. Using these makes it easier to for example change class
names around.
Self alias types:
There are also the Self and SelfClass types inside your .c file. These
serve the same function as the above, they make it easier to type and
easier to change typenames around which can help a lot during prototyp‐
ing stage. However you should note that the Self type should not be
used in function prototypes as one of the arguments or as a return
value type. This is because this is a simple C typedef which is only
available inside your .c file and not in the header files. You can
disable both the self casting macros and the self type aliases by pass‐
ing --no-self-alias to gob.
DEALING WITH DIFFERENT GOB VERSIONS
Defines:
In your generated C file, you can use the defines GOB_VERSION_MAJOR
GOB_VERSION_MINOR and GOB_VERSION_PATCHLEVEL if you wish to for example
use a feature that is only available in some newer gob version. Note
however that you can only use these defines in the C code portions of
your .gob file, and #ifdef´s cannot span multiple functions. Check the
BUGS section for more on using the C preprocessor and gob.
Minimum version requires:
You can also make your .gob file require at least certain version of
gob. You do this by putting ´requires x.y.z´ (where x.y.z is the ver‐
sion number) outside of any C block, comment or class, usually you
should make this the first line in the file or close to the top. If
gob finds this and the version of gob used to compile the code is lower
then that listed in the require, gob will generate an error and exit.
For example to require that gob2 version 2.0.0 or higher be used to
compile a file, put this at the top of that file:
requires 2.0.0
CREATING NEW ENUM, FLAGS and ERROR TYPES
You can create new GObject ENUM, FLAGS and GError types for use in your
classes easily. Glib includes some utilities for handling these, how‐
ever it may be cleaner to use the below specified way in your classes.
It also then doesn´t require any Makefile setup. Make sure this is
defined in the same section as the class, that is not in any of the
´%?{´ ´%}´ sections.
You use the keywords ´enum´ ´flags´ and ´error´ as you would use the
´class´ keyword. Then you give a prefix for the values in the enumera‐
tion. Then you define a list of values just like in C. For ´enum´
types you can also specify the values assigned to each string. Then
you specify the type in the standard gob style of specifying types.
Here are a few examples of all of these:
enum LAME_CLIENT {
IS_CONNECTED,
NONE = 9,
LAST
} Test:Enum;
flags BUGA_BUGA {
ONE,
TWO,
MANY,
} Some:Flags;
error TEST_OBJECT_ERROR {
BAD_THIS,
BAD_THAT
} Test:Object:Error;
This will for example define an enum that is equivalent to the follow‐
ing C code:
typedef enum {
LAME_CLIENT_IS_CONNECTED,
LAME_CLIENT_NONE = 9,
LAME_CLIENT_LAST
} TestEnum;
C++ MODE
There is a C++ mode so that gob creates C++ compiler friendly files.
You need to use the --for-cpp argument to gob. This will make the gen‐
erated file have a .cc instead of a .c extension, and several things
will be adjusted to make it all work for a C++ compiler. One thing
that will be missing is an alias to the new method, as that clashes
with C++, so instead you´ll have to use the full name of the method
inside your code. Also note that gob does not use any C++ features,
this option will just make the generated code compile with a C++ com‐
piler.
OVERRIDING THE GET_TYPE METHOD
The get_type is not really a method, but a function which initializes
your object. Recently objects appeared which require you to make a
custom get_type function. So it is possible to override this function.
To do so, just define a new public method called get_type, with no
arguments. Example:
public GType
get_type (void)
{
/* code goes here */
return some_type;
}
INTERFACES
Currently gob will only allow you to implement interfaces (that is,
define new classes which implement an interface) and doesn´t yet have
support for making new interfaces, but this will be coming at some
point in the future.
To define a class that implements an interface add a class flag ´inter‐
face´ with the type name of the interface as an argument. Then to
implement a specific method of the interface, just add ´interface
<typename>´ before the method definition. The method can, and probably
should be, private.
The following example implements a new object, that implements the
Gtk:Tree:Model interface and implements the get_flags method of that
interface. Do note that except for standard (GTK+ and glib) specific
interfaces which seem to have a non-standard name for the interface
structure, the structure should end with and Iface, if you are imple‐
menting an interface. That is for example for the Gtk:Tree:Model, the
structure containing the table of methods should be named GtkTreeMod‐
elIface.
class Some:Object from G:Object
(interface Gtk:Tree:Model)
{
/* function implemented for the Gtk:Tree:Model interface */
interface Gtk:Tree:Model
private GtkTreeModelFlags
get_flags (Gtk:Tree:Model *self (check null type))
{
/* Here would be the implementation */
return (GtkTreeModelFlags)0;
}
}
If you want to implement multiple interfaces just list more class flag
lines as follows:
class Some:Object from G:Object
(interface Gtk:Tree:Model)
(interface Gtk:Editable)
{
/* ... */
}
DIRECT BonoboObject SUPPORT
If you want to build a BonoboObject class gob2 has direct support for
these. Just create a new object that derives from Bonobo:Object. Then
use a "BonoboObject" class flag with the interface name as an argument.
The interface name should be as you would type it in C, that is with
underscores as namespace separators. Then you add the methods (using
exact same names as in the idl file) and prepend those methods with a
BonoboObject keyword. For example imagine you have an interface
GNOME/Foo/SomeInterface, with a method fooBar that takes a single
string:
class Foo:Some:Interface from Bonobo:Object
(BonoboObject GNOME_Foo_SomeInterface) {
BonoboObject
private void
fooBar (PortableServer_Servant servant,
const CORBA_char *string,
CORBA_Environment *ev)
{
Self *self = SELF (bonobo_object_from_servant (servant));
/* your code here */
}
/* rest of class */
}
Note that the implementation method can be private, in fact that´s
probably a good idea to do. It won´t work to make this a signal, it
can however be a virtual. Note that the method prototype must match
the one from the interface header file, or you will get a bad assign‐
ment warning. You should check the header file generated by orbit-idl
and see the epv structure for the correct prototypes if you can´t fig‐
ure them out from the idl itself. Also note that the first argument is
not "self", but the servant and you must use bonobo_object_from_servant
function to get the actual object pointer.
DIRECT LIBGLADE SUPPORT
Gob can simplify writing a libglade class. Just create a new object
that derives from a GtkContainer widget. Then use a "GladeXML" class
flag with the glade file name, root widget and optional domain as
arguments between double quotes. For example:
class My:Glade from Gtk:Window (GladeXML "gob-libglade.glade" "root")
{
....
}
Note however that then "gob-libglade.glade" would have to be in the
current directory. You could specify a path, but that may not work for
all installations. You can replace the glade filename with a token to
be used in the generated .c file and you can then have a macro with the
filename, as follows:
class My:Glade from Gtk:Window (GladeXML GLADE_FILE "root")
{
....
}
And somewhere in your header files you would have
#define GLADE_FILE "/path/to/file.glade"
You can declare widgets as data members by adding a 'GladeXML' to the
definition.
private Gtk:Button * button1 GladeXML;
This will automatically set the "button1" from the GladeXML file.
All signals created with glade are automatically connected if you
defined those class methods in your class. For example suppose in
glade that we set the "connect" signal on button1 to go to on_but‐
ton1_clicked, then in our gob file we can just write:
public void
on_button1_clicked(self, GtkButton * button)
{
}
See the examples directory for a full example. Note that this feature
requires version at least 2.0.12.
IDENTIFIER CONFLICTS
Gob will need to define some local variables and functions in the gen‐
erated files, so you need to take some precaution not to conflict with
these. The general rule of thumb is that all of these start with three
underscores. There is one, "parent_class" which doesn´t because it´s
intended for use in your code. For virtuals or signals, you cannot use
the identifier __parent__ which is used for the parent of the object.
You should actually never access __parent__ either as it not guaranteed
that it will stay named this way. Data members cannot be named __par‐
ent__ nor _priv. For methods, you cannot use the identifiers "init" or
"class_init" unless you mean the constructor methods. You shouldn´t
generally use 3 underscores even in override method argument lists and
virtual and signal method names as it might confuse the PARENT_HANDLER
macro. In fact avoiding all names with three underscores is the best
policy when working with gob.
There are a couple of defines which you shouldn´t be redefining in the
code or other headers. These are SELF, IS_SELF, SELF_CLASS, SELF_TYPE,
ARG, VAR, PARENT_HANDLER, GET_NEW, GOB_VERSION_MAJOR, GOB_VERSION_MINOR
and GOB_VERSION_PATCHLEVEL.
As for types, there are Self and SelfClass types which are only defined
in your source files. Their generation (just like the generation of
the SELF macros) can be turned off, see command line options.
USING GTK-DOC STYLE INLINE DOCUMENTATION
If you want to use gtk-doc style inline documentation for your objects,
you can do one of two things. First, you could include the inline doc‐
umentation comments in your %{ %} section which will then be put verba‐
tim into the output source file. This is the way you should use for
functions you define outside of the class.
For class methods, you should use a gtk+ style comment, however it can
be indented any number of tabs or spaces and you can use the short
method name without the type prefix. Gob will automatically try to
extract these and translate to full names and put them in the output
source file. An example would be:
class Gtk:Button:Example from Gtk:Button {
/**
* new:
*
* Makes a new #GtkButtonExample widget
*
* Returns: a new widget
**/
public
GtkWidget *
new(void)
{
return (GtkWidget *)GET_NEW;
}
}
If the function you are documenting is a signal or a virtual then it
will be documenting the wrapper that starts that virtual function or
emits that signal.
DEALING WITH CIRCULAR HEADERS
Sometimes you may need to use an object of type MyObjectA in the MyOb‐
jectB class and vice versa. Obviously you can´t include headers for
both. So you need to just declare the typedef in the header of A for
B, and the other way around as well. The headers generated include a
protecting define before it declares the typedef. This define is the
__TYPEDEF_<upper case object name>__. So inside my-object-a.h there
will be this:
#ifndef __TYPEDEF_MY_OBJECT_A__
#define __TYPEDEF_MY_OBJECT_A__
typedef struct _MyObjectA MyObjectA;
#endif
Now instead of including my-object-a.h in the header section of my-
object-b.gob, just copy the above code there and you´re set for using
MyObjectA as a type in the method parameters and public types.
Another way to get out of this problem is if you can use those types
only in the private members, in which case they won´t be in the gener‐
ated public header.
BUILDING WITH MAKE
If you are using normal makefiles, what you need to do is to add a
generic rule for .gob files. So you would include the following in the
Makefile and then just use the .c and .h files as usual (make sure the
space before the ´gob2´ is a tab, not spaces):
%.c %.h %-private.h: %.gob
gob2 $<
BUILDING WITH AUTOCONF and AUTOMAKE
This is a little bit more involved. Basically the first thing to do is
to check for GOB2 in your configure.in file. You can use the supplied
m4 macro which will also check the version of gob. Basically you
include this:
GOB2_CHECK([2.0.0])
This will replace @GOB2@ in your makefiles with the full path of gob2.
Thus when adding the generic rule to your Makefile.am file, it should
look like:
%.c %.h %-private.h: %.gob
@GOB2@ $<
For Makefile.am you have to set up a couple more things. First you
have to include the generated .c and .h files into BUILT_SOURCES vari‐
able. You have to include both the .gob and the .c and .h files in the
SOURCES for your program.
PREVENTING SPURIOUS BUILDS
When nothing has changed you might not really want to rebuild every‐
thing and gob provides options --no-touch (since 2.0.13) and --no-
touch-headers to avoid this. When working with build systems such as
automake you have to be more careful as just using those options can
cause automake to get confused and you will need to use something like
the following:
foo_SOURCES = foo.gob foo.gob.stamp foo.c foo.h foo-private.h
BUILT_SOURCES = foo.gob.stamp
MAINTAINERCLEANFILES = foo.gob.stamp
%.gob.stamp: %.gob
@GOB2@ --no-touch $<
@touch $@
DEBUGGING
GOB does several things to make debugging the code easier. First it
adds preprocessor commands into the output c file that point to the
correct places in your .gob input file. However sometimes there might
be some bigger confusion and this is just not helpful. In this case
you will probably want to have gcc point you directly at the generated
files. For this use the --no-lines command line option. You should
also note that these commands are not generated for the public header
file at all. If there is an error which points you to the public
header file, make sure you fix this error in the .gob file, otherwise
your changes will not have any effect after gob recompiles the sources
again.
Sometimes you might want to know which method you are in for some
debugging output. GOB will define __GOB_FUNCTION__ macro, which is
just a string constant with a pretty name of the method.
M4 SUPPORT
It is possible to have your .gob file also preprocessed by m4. This is
useful if you have a lot of files and you´d like to have some pre‐
processor put in some common features. All you have to do is add --m4
to the command line of gob2 and gob2 will first run your file through
m4. You can print the directory that is searched for m4 files by run‐
ning "gob2 --m4-dir"
All the arguments after --m4 will be passed to m4 itself, so it has to
be the last gob2 argument on the command line. This way you can spec‐
ify arbitrary options to pass to m4.
BUGS
The lexer does not actually parse the C code, so I´m sure that some
corner cases or maybe even some not so corner cases of C syntax might
confuse gob completely. If you find any, send me the source that makes
it go gaga and I´ll try to make the lexer try to handle it properly,
but no promises.
Another thing is that gob ignores preprocessor macros. Since gob
counts braces, the following code won´t work:
#ifdef SOME_DEFINE
if(foo) {
#else
if(bar) {
#endif
blah();
}
To make this work, you´d have to do this:
#ifdef SOME_DEFINE
if(foo)
#else
if(bar)
#endif
{
blah();
}
There is no real good way we can handle this without parsing C code, so
we probably never will. In the future, I might add #if 0 as a comment
but that´s about as far as I can really take it and even that is prob‐
lematic. Basically, if you use gob, just don´t use the C preprocessor
too extensively. And if you use it make sure that you do not cross the
boundaries of the C code segments.
Comments will not get through to the generated files unless inside C
code. This is not the case for gtk-doc style comments which are sup‐
ported.
The short name aliases are actually implemented as pointers to func‐
tions. Thus if you want to get the pointer of a function using the
short name alias you can´t use the ´&´. Thus:
void (*foo)(Self *);
/* this will NOT work */
foo = &self_short_name;
/* this will work */
foo = self_short_name;
/* Both of these will work */
foo = &my_class_long_name;
foo = my_class_long_name;
AUTHOR
George Lebl <jirka@5z.com>
GOB2 Homepage: http://www.jirka.org/gob.html
GOB2 2.0.14 GOB2(1)
