3 .\" (C) 1999 George Lebl <jirka@5z.com>
5 .\" This manual page is covered by the terms of the GNU General
10 GOB \- The GTK+ Object Builder
16 GTK+ Object Builder is a simple preprocessor for easily creating
17 GTK+ objects. It does not parse any C code and ignores any C errors. It
18 is in spirit similiar to things like lex or yacc.
21 Because we need to parse out different parts of the typename,
22 sometimes you need to specify the typename with some special syntax.
23 Types are specified in capitalized form and words are separated by ':'.
24 The first word of the type (which can be empty) is the "namespace". This
25 fact is for example used for the type checking macro. For "Gtk:New:Button",
26 the macro will be GTK_IS_NEW_BUTTON. This format of typenames is used in
27 the class declaration header and for method argument types.
31 The filenames are created from the typename. The words are
32 separated by '-' and all in lower case. For example for an object named
33 "Gtk:New:Button", the files are gtk-new-button.c and gtk-new-button.h.
35 .SH INCLUDING NORMAL C CODE IN THE OUTPUT FILES
37 To include some code directly in the output C file begin with
38 '%{' on an empty line and end the code with a '%{' on an empty line. To
39 put the code in the output header file, start the code with a '%h{'.
54 .SH MAKING A NEW CLASS
58 There can be only one class per input file. Defining a class
59 is sort of like in Java, you define the class and write inline code
60 directly into the class definition. To define a class you need to specify
61 the new object name and the name of the object from which it is derived
62 from, such as this "class <new type> from <parent type> { <class code> }".
66 class Gtk:New:Button from Gtk:Button {
74 There are three types of data members. Two of them are normal
75 data numbers, and one is a virtual one, usually linked to a normal public
76 data member. The two normal data members are public or private. They are
77 basically just copied into the object directly. There is only one
78 identifier allowed per typename unlike in normal C. Example:
86 The private members are not currently protected from outside use,
87 they are just marked by a comment in the header file, this will most likely
88 be somehow solved in some future version.
90 The third type is an argument type. It is a named datamember which
91 is one of the features of the GTK+ object system. You need to define a get
92 and a set handler. They are fragments of C code that will be used to
93 get the value orset the value of the argument. Inside them you can use the
94 define ARG to which you assign the data or get the data. You can also use
95 the identifier "this" as pointer to the object instance. The type is
96 defined as one of the gtk type enums, but without the GTK_TYPE_ prefix.
101 argument INT height set { this->height = ARG; } get { ARG = this->height; };
105 If you don't define a set or a get handler it will be a readonly
106 or a writeonly argument. If you want to add extra argument flags, add
107 them into parenthesis after the argument keyword, separated by '|' and
108 without the GTK_ARG_ prefix. For example:
112 argument (CONSTRUCT) INT height get { ARG = this->height; };
118 There is a whole array of possible methods. The two normal,
119 "familiar" method types are private and public. Public are defined as
120 normal functions with a prototype in the header file. Private methods
121 are defined as static functions with prototypes at the top of the .c
122 file. Then there are signal, virtual and override methods. You can also
123 define init and init_class methods with a special definition if you want
124 to add code to the constructors or you can just leave them out.
128 For all but the init and init_class methods, you use the
129 following syntax for arguments. The first argument can be just "this",
130 which gob will translateinto a pointer to the object instance. The rest
131 of the arguments are very similiar to normal C arguments. If the
132 typename is an object pointer you should use the syntax defined above
133 with the words separated by ':'
137 <type> <argument id> (check <list of checks>)
140 The checks are glib type preconditions, and can be the following:
141 "null", which tests pointers for being NULL, "type" which checks GTK+
142 object pointers for being the right type, "<test> <number>" which tests
143 numberic arguments for being a certain value. The test can be a <,>,<=,>=
147 public int foo(this, int h (check > 0 < 11), Gtk:Widget *w (check null type))
151 This will be the prototype of a function which has a this pointer
152 as the first argument, an integer argument which will be checked and has
153 to be more then 0 and less then 11, and a pointer to a GtkWidget object
154 instance and it is checked for being null and the type will also be
159 Methods which have a return value, there also has to be something
160 returned if there is an error, such as if a precondition is not met. The
161 default is 0, casted to the type of the method. If you need to return
162 something else then you can specify an "onerror" keyword after the
163 prototype and after that a number, a token (an identifier) or a bit of C
164 code enclosed in braces {}. The braces will not be printed into the
165 output, they just delimit the string. For example
168 public void * get_something(this, int i (check >= 0)) onerror NULL {
176 Virtual methods are basically pointers in the class structure,
177 so that one can override the method in derived methods. They can be empty
178 (if you put ';' instead of the C code). A wrapper will also be defined
179 which makes calling the methods he same as public methods. This type of
180 method is just a little bit "slower" then normal functions, but not as
181 slow as signals. You define them by using "virutal" keywrod before the
186 Signals are methods to which the user can bind other handlers
187 and override the default handler. The default handler is basically the
188 method body. This is the most versatile and flexible type of a method
189 and also the slowest. You need to specify a whole bunch of things when
190 you define a signal. One thing is when the default handler will be run,
191 first or last. You specify that by "first" or "last" right after the
192 "signal" keyword. Then you need to define the gtk enum types (again
193 without the GTK_TYPE_ prefix). For that you define the return types
194 and the types of arguments after the "this" pointer (not including the
195 "this" pointer). You put it in the following syntax "<return type> (<list
196 of arguments>)". If the return type is void, the type should be "NONE",
197 the same should be for the argument list. The rest of the prototype is
198 the same as for other method types. The body can also be empty, and
199 also there is a public method wrapper which you can use for calling the
200 signal jus tlike a public method. Example:
203 signal first INT(POINTER,INT)
204 int do_something(this, Gtk:Widget *w (check null type), int length)
211 signal last NONE(NONE) void foo(this);
217 If you need to override some method (a signal or a virtual method
218 of some class in the parent tree of the new object), you can define and
219 override method. After the "override" keyword, you should put the
220 typename of the class you are overriding a method from. Other then that
221 it is the same as for other methods. The "this" pointer in this case
222 should be the type of the method you are overriding so that you don't
223 get warnings during compilation. Example:
226 override (Gtk:Container) void
227 add (Gtk:Container *this (check null type), Gtk:Widget *wid (check null type))
235 Inside the code, defines are set for the methods, so that you don't
236 have to type the class name before each call. Example:
248 return foo(this) + i;
253 The generated header file is included as the first file in the .c file, no
254 matter what. ths means that you willhave to putthings that need to be included
255 before that, into an %h{ } section.
258 George Lebl <jirka@5z.com>