NAME¶
GOB2 - The GObject Builder
SYNOPSIS¶
gob2 [ 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 creating 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 PREVENTING
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. Private 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 without 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
character is given then none is used. Only one character can be used.
- --gtk3
- Use gtk3.
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
<basename>-private.h (for the example above it would be
gtk-new-button-private.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 created 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 ´privateheader´ 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. When you want code to appear as in alltop but
only in the cfile you use the ´ctop´ (or ´ct´)
section. Note that ctop requires 2.0.18. Finally, ´afterdecls´
includes code between the declarations and the method implementations, but
note that ´afterdecls´ requires version 2.0.16. For example:
%alltop{
/* this will be at the very top of all output files */
%}
%ctop{
/* this will be at the very top of the C file */
/* Requires 2.0.18 */
%}
%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 */
%}
%afterdecls{
/* between the declarations and the method implementations */
/* Requires gob version 2.0.16 */
%}
%{
/* 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 automatically includes the public header
file, and thus the public header file will be indirectly included at the very
top of the file.
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. Public 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 identifier 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 functionality 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 can use the SELF_GET_CLASS macro (or
YOUR_OBJECT_NAME_GET_CLASS) to get at the class. Thus the following would
work:
SELF_GET_CLASS(object)->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 followed by arbitrary code in
curly braces. Inside this code a macro called VAR will be define which refers
to your variable. So for example 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 debugging 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 destructors 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 argument. 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
(
name = "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.
The ´name´ property is canonical name of property. It is useful
when you try to implement properties with no C names like
´vertical-scroll´. The ´name´ property can be
omitted.
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 handler
will be run automatically with this value). This value will be overridden 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
enumeration 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 standard 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 automatically 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 argument. 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 compilers. The
code will compile on other compilers but with minimal type safety. For
complete type safety it is useful to use the get/set methods that are defined
by using the ´export´ attribute.
To get bettery type safety on some of the property types, you can specify 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,
"familiar" method types are private, protected and public. Public
are defined as normal functions with a prototype in the header file. Protected
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 methods. 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 constructors 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 public, 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 syntax 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.
Function attributes:
For method that aren't virtual, signal or override methods, and aren't init or
class_init, GLib function attribute macros G_GNUC_PRINTF, G_GNUC_SCANF, and
G_GNUC_FORMAT can optionally be included after the argument list. Simply
include an ´attr´ keyword and the C code to include in the file.
You have to include braces and anything inside the braces will be printed into
the header file after the function declaration and before the trailing
semicolon. The braces themselves are not printed. For example:
public void
print (self, const char *format (check null), ...)
attr {G_GNUC_PRINTF(2, 3)}
This will produce a prototype which will generate a warning at compile time if
the contents of the format argument (argument number 2) aren't consistent with
the types and number of the subsequent variadic arguments (the first of which
is argument number 3). Only one ´attr´ keyword per method is
allowed. If you have more than one attribute to include, you should put them
all within the braces. Note that function attributes were aded in version
2.0.16.
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 any
optional function attribute macros, 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 identical
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 function
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.
Constructor, dispose, finalize methods:
Since 2.0.16, you can also easily add code to the object's constructor, dispose,
and finalize methods. See GObject documentation on how these are run. The code
you add will be run before calling the parents function for dispose and
finalize, and after the parent function for constructor. The syntax is just
like init and class_init. For example:
constructor (self) {
/* constructor method */
}
dispose (self) {
/* dispose method */
}
finalize (self) {
/* finalize method */
}
You can also just override those methods as usual, but the above is much easier
and nearly as flexible.
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 little 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 override 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 including 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);
You can include name of signal, if this name is not a C variable name. Example:
signal first INT "do-something" (POINTER, INT)
int do_something (self, Gtk:Widget *w (check null type), int length)
{
...
}
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 compiler 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_connect_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 expression 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 executed 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 prototyping 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 passing --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 version
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, however 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 enumeration. 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 following 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 generated 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++
compiler.
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
´interface´ 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 implementing an interface.
That is for example for the Gtk:Tree:Model, the structure containing the table
of methods should be named GtkTreeModelIface.
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 assignment warning. You
should check the header file generated by orbit-idl and see the epv structure
for the correct prototypes if you can´t figure 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_button1_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 generated
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 __parent__ 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 documentation
comments in your %{ %} section which will then be put verbatim 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.
Sometimes you may need to use an object of type MyObjectA in the MyObjectB 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 generated 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 variable. 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 everything 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 preprocessor 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 running "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 specify 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
problematic. 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 supported.
The short name aliases are actually implemented as pointers to functions. 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