[gob-dx.git] / doc / USER_GUIDE

GTK+ Object Builder

AUTHOR: George Lebl

        GTK+ Object Builder is a simple preprocessor for easily creating
GTK+ objects.  It does not parse any C code and ignores any C errors.  It
is in spirit similiar to things like lex or yacc.

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.  For "Gtk:New:Button",
the macro will be GTK_IS_NEW_BUTTON.  This format of typenames is used in
the class declaration header and for method argument types.

The output file names:

        The filenames are created from the typename.  The words are
separated by '-' 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.

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.  To
put the code in the output header file, start the code with a '%h{'.
For example:

%h{
void somefunc(int i);
%}
%{
void somefunc(int i)
{
        /* some code */
}
%}

Making a new class:

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>
}

Data members:

        There are three types of data members.  Two of them are normal
data numbers, and one is a virtual one, usually linked to a normal public
data member.  The two normal data members are public or private. They are
basically just copied into the object directly.  There is only one
identifier allowed per typename unlike in normal C.  Example:

public int i;
private GtkWidget *h;

        The private members are not currently protected from outside use,
they are just marked by a comment in the header file, this will most likely
be somehow solved in some future version.

        The third type is an argument type.  It is a named datamember which
is one of the features of the GTK+ object system.  You need to define a get
and a set handler.  They are fragments of C code that will be used to 
get the value orset the value of the argument.  Inside them you can use the
define ARG to which you assign the data or get the data.  You can also use
the identifier "this" as pointer to the object instance.  The type is
defined as one of the gtk type enums, but without the GTK_TYPE_ prefix.
For example:

public int height;
argument INT height set { this->height = ARG; } get { ARG = this->height; };

        If you don't define a set or a get handler it will be a readonly
or a writeonly argument.  If you want to add extra argument flags, add
them into parenthesis after the argument keyword, separated by '|' and
without the GTK_ARG_ prefix.  For example:

public int height;
argument (CONSTRUCT) INT height get { ARG = this->height; };

Methods:

        There is a whole array of possible methods.  The two normal,
"familiar" method types are private and public.  Public are defined as
normal functions with a prototype in the 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.  You can also
define init and init_class methods with a special definition if you want
to add code to the constructors or you can just leave them out.

Argument lists:

        For all but the init and init_class methods, you use the
following syntax for arguments.  The first argument can be just "this",
which gob will translateinto a pointer to the object instance.  The rest
of the arguments are very similiar 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
numberic arguments for being a certain value.  The test can be a <,>,<=,>=
!= or ==.  Example:

public int foo(this, int h (check > 0 < 11), Gtk:Widget *w (check null type))

        This will be the prototype of a function which has a this 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(this, int i (check >= 0)) onerror NULL {
        ...
}

Virtual methods:

        Virtual methods are basically pointers in the class structure,
so that one can override the method in derived methods.  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 "virutal" keywrod before the
prototype.

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 gtk enum types (again
without the GTK_TYPE_ prefix).  For that you define the return types
and the types of arguments after the "this" pointer (not including the
"this" 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 jus tlike a public method.  Example:

signal first INT(POINTER,INT)
int do_something(this, Gtk:Widget *w (check null type), int length)
{
        ...
}

or

signal last NONE(NONE) void foo(this);

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 "this" pointer in this case
should be the type of the method you are overriding so that you don't
get warnings during compilation.  Example:

override (Gtk:Container) void
add (Gtk:Container *this (check null type), Gtk:Widget *wid (check null type))
{
        ...
}

Calling methods:

        Inside the code, defines are set for the methods, so that you don't
have to type the class name before each call.  Example:

private int
foo(this)
{
        return this->len;
}

private int
bar(this,int i)
{
        return foo(this) + i;
}