1Glib::Object::IntrospecUtsieorn(C3o)ntributed Perl DocumGelnitba:t:iOobnject::Introspection(3)
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NAME

6       Glib::Object::Introspection - Dynamically create Perl language bindings
7

SYNOPSIS

9         use Glib::Object::Introspection;
10         Glib::Object::Introspection->setup(
11           basename => 'Gtk',
12           version => '3.0',
13           package => 'Gtk3');
14         # now GtkWindow, to mention just one example, is available as
15         # Gtk3::Window, and you can call gtk_window_new as Gtk3::Window->new
16

ABSTRACT

18       Glib::Object::Introspection uses the gobject-introspection and libffi
19       projects to dynamically create Perl bindings for a wide variety of
20       libraries.  Examples include gtk+, webkit, libsoup and many more.
21

DESCRIPTION FOR LIBRARY USERS

23       To allow Glib::Object::Introspection to create bindings for a library,
24       the library must have installed a typelib file, for example
25       "$prefix/lib/girepository-1.0/Gtk-3.0.typelib".  In your code you then
26       simply call "Glib::Object::Introspection->setup" with the following
27       key-value pairs to set everything up:
28
29       basename => $basename
30           The basename of the library that should be wrapped.  If your
31           typelib is called "Gtk-3.0.typelib", then the basename is 'Gtk'.
32
33       version => $version
34           The particular version of the library that should be wrapped, in
35           string form.  For "Gtk-3.0.typelib", it is '3.0'.
36
37       package => $package
38           The name of the Perl package where every class and method of the
39           library should be rooted.  If a library with basename 'Gtk'
40           contains an class 'GtkWindow', and you pick as the package 'Gtk3',
41           then that class will be available as 'Gtk3::Window'.
42
43       The Perl wrappers created by "Glib::Object::Introspection" follow the
44       conventions of the Glib module and old hand-written bindings like Gtk2.
45       You can use the included tool "perli11ndoc" to view the documentation
46       of all installed libraries organized and displayed in accordance with
47       these conventions.  The guiding principles underlying the conventions
48       are described in the following.
49
50   Namespaces and Objects
51       The namespaces of the C libraries are mapped to Perl packages according
52       to the "package" option specified, for example:
53
54         gtk_ => Gtk3
55         gdk_ => Gtk3::Gdk
56         gdk_pixbuf_ => Gtk3::Gdk::Pixbuf
57         pango_ => Pango
58
59       Classes, interfaces and boxed and fundamental types get their own
60       namespaces, in a way, as the concept of the GType is completely
61       replaced in the Perl bindings by the Perl package name.
62
63         GtkButton => Gtk3::Button
64         GdkPixbuf => Gtk3::Gdk::Pixbuf
65         GtkScrolledWindow => Gtk3::ScrolledWindow
66         PangoFontDescription => Pango::FontDescription
67
68       With this package mapping and Perl's built-in method lookup, the
69       bindings can do object casting for you.  This gives us a rather
70       comfortably object-oriented syntax, using normal Perl object semantics:
71
72         in C:
73           GtkWidget * b;
74           b = gtk_check_button_new_with_mnemonic ("_Something");
75           gtk_toggle_button_set_active (GTK_TOGGLE_BUTTON (b), TRUE);
76           gtk_widget_show (b);
77
78         in Perl:
79           my $b = Gtk3::CheckButton->new_with_mnemonic ('_Something');
80           $b->set_active (1);
81           $b->show;
82
83       You see from this that cast macros are not necessary and that you don't
84       need to type namespace prefixes quite so often, so your code is a lot
85       shorter.
86
87   Flags and Enums
88       Flags and enum values are handled as strings, because it's much more
89       readable than numbers, and because it's automagical thanks to the GType
90       system.  Values are referred to by their nicknames; basically, strip
91       the common prefix, lower-case it, and optionally convert '_' to '-':
92
93         GTK_WINDOW_TOPLEVEL => 'toplevel'
94         GTK_BUTTONS_OK_CANCEL => 'ok-cancel' (or 'ok_cancel')
95
96       Flags are a special case.  You can't (sensibly) bitwise-or these
97       string-constants, so you provide a reference to an array of them
98       instead.  Anonymous arrays are useful here, and an empty anonymous
99       array is a simple way to say 'no flags'.
100
101         FOO_BAR_BAZ | FOO_BAR_QUU | FOO_BAR_QUUX => [qw/baz quu qux/]
102         0 => []
103
104       In some cases you need to see if a bit is set in a bitfield; methods
105       returning flags therefore return an overloaded object.  See Glib for
106       more details on which operations are allowed on these flag objects, but
107       here is a quick example:
108
109         in C:
110           /* event->state is a bitfield */
111           if (event->state & GDK_CONTROL_MASK) g_printerr ("control was down\n");
112
113         in Perl:
114           # $event->state is a special object
115           warn "control was down\n" if $event->state & "control-mask";
116
117       But this also works:
118
119         warn "control was down\n" if $event->state * "control-mask";
120         warn "control was down\n" if $event->state >= "control-mask";
121         warn "control and shift were down\n"
122                                   if $event->state >= ["control-mask", "shift-mask"];
123
124   Memory Handling
125       The functions for ref'ing and unref'ing objects and free'ing boxed
126       structures are not even mapped to Perl, because it's all handled
127       automagically by the bindings.  Objects will be kept alive so long as
128       you have a Perl scalar pointing to it or the object is referenced in
129       another way, e.g. from a container.
130
131       The only thing you have to be careful about is the lifespan of non
132       reference counted structures, which means most things derived from
133       "Glib::Boxed".  If it comes from a signal callback it might be good
134       only until you return, or if it's the insides of another object then it
135       might be good only while that object lives.  If in doubt you can
136       "copy".  Structs from "copy" or "new" are yours and live as long as
137       referred to from Perl.
138
139   Callbacks
140       Use normal Perl callback/closure tricks with callbacks.  The most
141       common use you'll have for callbacks is with the Glib "signal_connect"
142       method:
143
144         $widget->signal_connect (event => \&event_handler, $user_data);
145         $button->signal_connect (clicked => sub { warn "hi!\n" });
146
147       $user_data is optional, and with Perl closures you don't often need it
148       (see "Persistent variables with closures" in perlsub).
149
150       The userdata is held in a scalar, initialized from what you give in
151       "signal_connect" etc.  It's passed to the callback in usual Perl "call
152       by reference" style which means the callback can modify its last
153       argument, ie. $_[-1], to modify the held userdata.  This is a little
154       subtle, but you can use it for some "state" associated with the
155       connection.
156
157         $widget->signal_connect (activate => \&my_func, 1);
158         sub my_func {
159           print "activation count: $_[-1]\n";
160           $_[-1] ++;
161         }
162
163       Because the held userdata is a new scalar there's no change to the
164       variable (etc.) you originally passed to "signal_connect".
165
166       If you have a parent object in the userdata (or closure) you have to be
167       careful about circular references preventing parent and child being
168       destroyed.  See "Two-Phased Garbage Collection" in perlobj about this
169       generally.  Toplevel widgets like "Gtk3::Window" always need an
170       explicit "$widget->destroy" so their "destroy" signal is a good place
171       to break circular references.  But for other widgets it's usually
172       friendliest to avoid circularities in the first place, either by using
173       weak references in the userdata, or possibly locating a parent
174       dynamically with "$widget->get_ancestor".
175
176   Exception handling
177       Anything that uses GError in C will "croak" on failure, setting $@ to a
178       magical exception object, which is overloaded to print as the returned
179       error message.  The ideology here is that GError is to be used for
180       runtime exceptions, and "croak" is how you do that in Perl.  You can
181       catch a croak very easily by wrapping the function in an eval:
182
183         eval {
184           my $pixbuf = Gtk3::Gdk::Pixbuf->new_from_file ($filename);
185           $image->set_from_pixbuf ($pixbuf);
186         };
187         if ($@) {
188           print "$@\n"; # prints the possibly-localized error message
189           if (Glib::Error::matches ($@, 'Gtk3::Gdk::Pixbuf::Error',
190                                         'unknown-format')) {
191             change_format_and_try_again ();
192           } elsif (Glib::Error::matches ($@, 'Glib::File::Error', 'noent')) {
193             change_source_dir_and_try_again ();
194           } else {
195             # don't know how to handle this
196             die $@;
197           }
198         }
199
200       This has the added advantage of letting you bunch things together as
201       you would with a try/throw/catch block in C++ -- you get cleaner code.
202       By using Glib::Error exception objects, you don't have to rely on
203       string matching on a possibly localized error message; you can match
204       errors by explicit and predictable conditions.  See Glib::Error for
205       more information.
206
207   Output arguments, lists, hashes
208       In C you can only return one value from a function, and it is a common
209       practice to modify pointers passed in to simulate returning multiple
210       values.  In Perl, you can return lists; any functions which modify
211       arguments are changed to return them instead.
212
213       Arguments and return values that have the types GList or GSList or
214       which are C arrays of values will be converted to and from references
215       to normal Perl arrays.  The same holds for GHashTable and references to
216       normal Perl hashes.
217
218   Object class functions
219       Object class functions like "Gtk3::WidgetClass::find_style_propery" can
220       be called either with a package name or with an instance of the
221       package.  For example:
222
223         Gtk3::WidgetClass::find_style_property ('Gtk3::Button', 'image-spacing')
224
225         my $button = Gtk3::Button->new;
226         Gtk3::WidgetClass::find_style_property ($button, 'image-spacing')
227
228   Overriding virtual functions
229       When subclassing a gtk+ class or when implementing a gtk+ interface
230       with Glib::Object::Subclass, you can override any virtual functions
231       that the class has by simply defining sub routines with names obtained
232       by capitalizing the original names of the virtual functions.  So, for
233       example, if you implement a custom subclass of "Gtk3::CellRenderer" and
234       want to override its virtual function "render", you provide a sub
235       routine with the name "RENDER" in your package.
236
237         sub RENDER {
238           my ($cell, $cr, $widget, $background_area, $cell_area, $flags) = @_;
239           # do something
240         }
241

DESCRIPTION FOR LIBRARY BINDING AUTHORS

243   "Glib::Object::Introspection->setup"
244       "Glib::Object::Introspection->setup" takes a few optional arguments
245       that augment the generated API:
246
247       search_path => $search_path
248           A path that should be used when looking for typelibs.  If you use
249           typelibs from system directories, or if your environment contains a
250           properly set "GI_TYPELIB_PATH" variable, then this should not be
251           necessary.
252
253       name_corrections => { auto_name => new_name, ... }
254           A hash ref that is used to rename functions and methods.  Use this
255           if you don't like the automatically generated mapping for a
256           function or method.  For example, if "g_file_hash" is automatically
257           represented as "Glib::IO::file_hash" but you want
258           "Glib::IO::File::hash" then pass
259
260             name_corrections => {
261               'Glib::IO::file_hash' => 'Glib::IO::File::hash'
262             }
263
264       class_static_methods => [ function1, ... ]
265           An array ref of function names that you want to be treated as
266           class-static methods.  That is, if you want be able to call
267           "Gtk3::Window::list_toplevels" as "Gtk3::Window->list_toplevels",
268           then pass
269
270             class_static_methods => [
271               'Gtk3::Window::list_toplevels'
272             ]
273
274           The function names refer to those after name corrections.
275
276       flatten_array_ref_return_for => [ function1, ... ]
277           An array ref of function names that return an array ref that you
278           want to be flattened so that they return plain lists.  For example
279
280             flatten_array_ref_return_for => [
281               'Gtk3::Window::list_toplevels'
282             ]
283
284           The function names refer to those after name corrections.
285           Functions occurring in "flatten_array_ref_return_for" may also
286           occur in "class_static_methods".
287
288       handle_sentinel_boolean_for => [ function1, ... ]
289           An array ref of function names that return multiple values, the
290           first of which is to be interpreted as indicating whether the rest
291           of the returned values are valid.  This frequently occurs with
292           functions that have out arguments; the boolean then indicates
293           whether the out arguments have been written.  With
294           "handle_sentinel_boolean_for", the first return value is taken to
295           be the sentinel boolean.  If it is true, the rest of the original
296           return values will be returned, and otherwise an empty list will be
297           returned.
298
299             handle_sentinel_boolean_for => [
300               'Gtk3::TreeSelection::get_selected'
301             ]
302
303           The function names refer to those after name corrections.
304           Functions occurring in "handle_sentinel_boolean_for" may also occur
305           in "class_static_methods".
306
307       use_generic_signal_marshaller_for => [ [package1, signal1,
308       [arg_converter1]], ... ]
309           Use an introspection-based generic signal marshaller for the signal
310           "signal1" of type "package1".  If given, use the code reference
311           "arg_converter1" to convert the arguments that are passed to the
312           signal handler.  In contrast to Glib's normal signal marshaller,
313           the generic signal marshaller supports, among other things, pointer
314           arrays and out arguments.
315
316       reblessers => { package => \&reblesser, ... }
317           Tells G:O:I to invoke reblesser whenever a Perl object is created
318           for an object of type package.  Currently, this only applies to
319           boxed unions.  The reblesser gets passed the pre-created Perl
320           object and needs to return the modified Perl object.  For example:
321
322             sub Gtk3::Gdk::Event::_rebless {
323               my ($event) = @_;
324               return bless $event, lookup_real_package_for ($event);
325             }
326
327   "Glib::Object::Introspection->invoke"
328       To invoke specific functions manually, you can use the low-level
329       "Glib::Object::Introspection->invoke".
330
331         Glib::Object::Introspection->invoke(
332           $basename, $namespace, $function, @args)
333
334       ·   $basename is the basename of a library, like 'Gtk'.
335
336       ·   $namespace refers to a namespace inside that library, like
337           'Window'.  Use undef here if you want to call a library-global
338           function.
339
340       ·   $function is the name of the function you want to invoke.  It can
341           also refer to the name of a constant.
342
343       ·   @args are the arguments that should be passed to the function.  For
344           a method, this should include the invocant.  For a constructor,
345           this should include the package name.
346
347       "Glib::Object::Introspection->invoke" returns whatever the function
348       being invoked returns.
349
350   Overrides
351       To override the behavior of a specific function or method, create an
352       appropriately named sub in the correct package and have it call
353       "Glib::Object::Introspection->invoke".  Say you want to override
354       "Gtk3::Window::list_toplevels", then do this:
355
356         sub Gtk3::Window::list_toplevels {
357           # ...do something...
358           my $ref = Glib::Object::Introspection->invoke (
359                       'Gtk', 'Window', 'list_toplevels',
360                       @_);
361           # ...do something...
362           return wantarray ? @$ref : $ref->[$#$ref];
363         }
364
365       The sub's name and package must be those after name corrections.
366
367   Converting a Perl variable to a GValue
368       If you need to marshal into a GValue, then Glib::Object::Introspection
369       cannot do this automatically because the type information is missing.
370       If you do have this information in your module, however, you can use
371       Glib::Object::Introspection::GValueWrapper to do the conversion.  In
372       the wrapper for a function that expects a GValue, do this:
373
374         ...
375         my $type = ...; # somehow get the package name that
376                         # corresponds to the correct GType
377         my $wrapper =
378           Glib::Object::Introspection::GValueWrapper->new ($type, $value);
379         # now use Glib::Object::Introspection->invoke and
380         # substitute $wrapper where you'd use $value
381         ...
382
383       If you need to call a function that expects an already set-up GValue
384       and modifies it, use "get_value" on the wrapper afterwards to obtain
385       the value.  For example:
386
387         my $wrapper =
388           Glib::Object::Introspection::GValueWrapper->new ('Glib::Boolean', 0);
389         $box->child_get_property ($label, 'expand', $gvalue);
390         my $value = $gvalue->get_value
391
392   Handling raw enumerations and flags
393       If you need to handle raw enumerations/flags or extendable enumerations
394       for which more than the pre-defined values might be valid, then use
395       "Glib::Object::Introspection->convert_enum_to_sv",
396       "Glib::Object::Introspection->convert_sv_to_enum",
397       "Glib::Object::Introspection->convert_flags_to_sv" and
398       "Glib::Object::Introspection->convert_sv_to_flags".  They will raise an
399       exception on unknown values; catching it then allows you to implement
400       fallback behavior.
401
402         Glib::Object::Introspection->convert_enum_to_sv (package, enum_value)
403         Glib::Object::Introspection->convert_sv_to_enum (package, sv)
404
405         Glib::Object::Introspection->convert_flags_to_sv (package, flags_value)
406         Glib::Object::Introspection->convert_sv_to_flags (package, sv)
407

SEE ALSO

409       perl-Glib: Glib
410       gobject-introspection: <http://live.gnome.org/GObjectIntrospection>
411       libffi: <http://sourceware.org/libffi/>
412

AUTHORS

414       Emmanuele Bassi <ebassi at linux intel com>
415       muppet <scott asofyet org>
416       Torsten Schönfeld <kaffeetisch at gmx de>
417

LICENSE

419       This library is free software; you can redistribute it and/or modify it
420       under the terms of the Lesser General Public License (LGPL).  For more
421       information, see http://www.fsf.org/licenses/lgpl.txt
422
423
424
425perl v5.30.0                      2019-07-26    Glib::Object::Introspection(3)
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