Provided by: libglib-object-introspection-perl_0.040-2_amd64 
NAME
Glib::Object::Introspection - Dynamically create Perl language bindings
SYNOPSIS
use Glib::Object::Introspection;
Glib::Object::Introspection->setup(
basename => 'Gtk',
version => '3.0',
package => 'Gtk3');
# now GtkWindow, to mention just one example, is available as
# Gtk3::Window, and you can call gtk_window_new as Gtk3::Window->new
ABSTRACT
Glib::Object::Introspection uses the gobject-introspection and libffi projects to
dynamically create Perl bindings for a wide variety of libraries. Examples include gtk+,
webkit, libsoup and many more.
DESCRIPTION FOR LIBRARY USERS
To allow Glib::Object::Introspection to create bindings for a library, the library must
have installed a typelib file, for example "$prefix/lib/girepository-1.0/Gtk-3.0.typelib".
In your code you then simply call "Glib::Object::Introspection->setup" with the following
key-value pairs to set everything up:
basename => $basename
The basename of the library that should be wrapped. If your typelib is called
"Gtk-3.0.typelib", then the basename is 'Gtk'.
version => $version
The particular version of the library that should be wrapped, in string form. For
"Gtk-3.0.typelib", it is '3.0'.
package => $package
The name of the Perl package where every class and method of the library should be
rooted. If a library with basename 'Gtk' contains an class 'GtkWindow', and you pick
as the package 'Gtk3', then that class will be available as 'Gtk3::Window'.
The Perl wrappers created by "Glib::Object::Introspection" follow the conventions of the
Glib module and old hand-written bindings like Gtk2. You can use the included tool
"perli11ndoc" to view the documentation of all installed libraries organized and displayed
in accordance with these conventions. The guiding principles underlying the conventions
are described in the following.
Namespaces and Objects
The namespaces of the C libraries are mapped to Perl packages according to the "package"
option specified, for example:
gtk_ => Gtk3
gdk_ => Gtk3::Gdk
gdk_pixbuf_ => Gtk3::Gdk::Pixbuf
pango_ => Pango
Classes, interfaces and boxed and fundamental types get their own namespaces, in a way, as
the concept of the GType is completely replaced in the Perl bindings by the Perl package
name.
GtkButton => Gtk3::Button
GdkPixbuf => Gtk3::Gdk::Pixbuf
GtkScrolledWindow => Gtk3::ScrolledWindow
PangoFontDescription => Pango::FontDescription
With this package mapping and Perl's built-in method lookup, the bindings can do object
casting for you. This gives us a rather comfortably object-oriented syntax, using normal
Perl object semantics:
in C:
GtkWidget * b;
b = gtk_check_button_new_with_mnemonic ("_Something");
gtk_toggle_button_set_active (GTK_TOGGLE_BUTTON (b), TRUE);
gtk_widget_show (b);
in Perl:
my $b = Gtk3::CheckButton->new_with_mnemonic ('_Something');
$b->set_active (1);
$b->show;
You see from this that cast macros are not necessary and that you don't need to type
namespace prefixes quite so often, so your code is a lot shorter.
Flags and Enums
Flags and enum values are handled as strings, because it's much more readable than
numbers, and because it's automagical thanks to the GType system. Values are referred to
by their nicknames; basically, strip the common prefix, lower-case it, and optionally
convert '_' to '-':
GTK_WINDOW_TOPLEVEL => 'toplevel'
GTK_BUTTONS_OK_CANCEL => 'ok-cancel' (or 'ok_cancel')
Flags are a special case. You can't (sensibly) bitwise-or these string-constants, so you
provide a reference to an array of them instead. Anonymous arrays are useful here, and an
empty anonymous array is a simple way to say 'no flags'.
FOO_BAR_BAZ | FOO_BAR_QUU | FOO_BAR_QUUX => [qw/baz quu qux/]
0 => []
In some cases you need to see if a bit is set in a bitfield; methods returning flags
therefore return an overloaded object. See Glib for more details on which operations are
allowed on these flag objects, but here is a quick example:
in C:
/* event->state is a bitfield */
if (event->state & GDK_CONTROL_MASK) g_printerr ("control was down\n");
in Perl:
# $event->state is a special object
warn "control was down\n" if $event->state & "control-mask";
But this also works:
warn "control was down\n" if $event->state * "control-mask";
warn "control was down\n" if $event->state >= "control-mask";
warn "control and shift were down\n"
if $event->state >= ["control-mask", "shift-mask"];
Memory Handling
The functions for ref'ing and unref'ing objects and free'ing boxed structures are not even
mapped to Perl, because it's all handled automagically by the bindings. Objects will be
kept alive so long as you have a Perl scalar pointing to it or the object is referenced in
another way, e.g. from a container.
The only thing you have to be careful about is the lifespan of non reference counted
structures, which means most things derived from "Glib::Boxed". If it comes from a signal
callback it might be good only until you return, or if it's the insides of another object
then it might be good only while that object lives. If in doubt you can "copy". Structs
from "copy" or "new" are yours and live as long as referred to from Perl.
Callbacks
Use normal Perl callback/closure tricks with callbacks. The most common use you'll have
for callbacks is with the Glib "signal_connect" method:
$widget->signal_connect (event => \&event_handler, $user_data);
$button->signal_connect (clicked => sub { warn "hi!\n" });
$user_data is optional, and with Perl closures you don't often need it (see "Persistent
variables with closures" in perlsub).
The userdata is held in a scalar, initialized from what you give in "signal_connect" etc.
It's passed to the callback in usual Perl "call by reference" style which means the
callback can modify its last argument, ie. $_[-1], to modify the held userdata. This is a
little subtle, but you can use it for some "state" associated with the connection.
$widget->signal_connect (activate => \&my_func, 1);
sub my_func {
print "activation count: $_[-1]\n";
$_[-1] ++;
}
Because the held userdata is a new scalar there's no change to the variable (etc.) you
originally passed to "signal_connect".
If you have a parent object in the userdata (or closure) you have to be careful about
circular references preventing parent and child being destroyed. See "Two-Phased Garbage
Collection" in perlobj about this generally. Toplevel widgets like "Gtk3::Window" always
need an explicit "$widget->destroy" so their "destroy" signal is a good place to break
circular references. But for other widgets it's usually friendliest to avoid
circularities in the first place, either by using weak references in the userdata, or
possibly locating a parent dynamically with "$widget->get_ancestor".
Miscellaneous
In C you can only return one value from a function, and it is a common practice to modify
pointers passed in to simulate returning multiple values. In Perl, you can return lists;
any functions which modify arguments are changed to return them instead.
Arguments and return values that have the types GList or GSList or which are C arrays of
values will be converted to and from references to normal Perl arrays. The same holds for
GHashTable and references to normal Perl hashes.
You don't need to specify string lengths. You can always use "substr" to pass different
parts of a string.
Anything that uses GError in C will "croak" on failure, setting $@ to a magical exception
object, which is overloaded to print as the returned error message. The ideology here is
that GError is to be used for runtime exceptions, and "croak" is how you do that in Perl.
You can catch a croak very easily by wrapping the function in an eval:
eval {
my $pixbuf = Gtk3::Gdk::Pixbuf->new_from_file ($filename);
$image->set_from_pixbuf ($pixbuf);
};
if ($@) {
print "$@\n"; # prints the possibly-localized error message
if (Glib::Error::matches ($@, 'Gtk3::Gdk::Pixbuf::Error',
'unknown-format')) {
change_format_and_try_again ();
} elsif (Glib::Error::matches ($@, 'Glib::File::Error', 'noent')) {
change_source_dir_and_try_again ();
} else {
# don't know how to handle this
die $@;
}
}
This has the added advantage of letting you bunch things together as you would with a
try/throw/catch block in C++ -- you get cleaner code. By using Glib::Error exception
objects, you don't have to rely on string matching on a possibly localized error message;
you can match errors by explicit and predictable conditions. See Glib::Error for more
information.
DESCRIPTION FOR LIBRARY BINDING AUTHORS
"Glib::Object::Introspection->setup"
"Glib::Object::Introspection->setup" takes a few optional arguments that augment the
generated API:
search_path => $search_path
A path that should be used when looking for typelibs. If you use typelibs from system
directories, or if your environment contains a properly set "GI_TYPELIB_PATH"
variable, then this should not be necessary.
name_corrections => { auto_name => new_name, ... }
A hash ref that is used to rename functions and methods. Use this if you don't like
the automatically generated mapping for a function or method. For example, if
"g_file_hash" is automatically represented as "Glib::IO::file_hash" but you want
"Glib::IO::File::hash" then pass
name_corrections => {
'Glib::IO::file_hash' => 'Glib::IO::File::hash'
}
class_static_methods => [ function1, ... ]
An array ref of function names that you want to be treated as class-static methods.
That is, if you want be able to call "Gtk3::Window::list_toplevels" as
"Gtk3::Window->list_toplevels", then pass
class_static_methods => [
'Gtk3::Window::list_toplevels'
]
The function names refer to those after name corrections.
flatten_array_ref_return_for => [ function1, ... ]
An array ref of function names that return an array ref that you want to be flattened
so that they return plain lists. For example
flatten_array_ref_return_for => [
'Gtk3::Window::list_toplevels'
]
The function names refer to those after name corrections. Functions occuring in
"flatten_array_ref_return_for" may also occur in "class_static_methods".
handle_sentinel_boolean_for => [ function1, ... ]
An array ref of function names that return multiple values, the first of which is to
be interpreted as indicating whether the rest of the returned values are valid. This
frequently occurs with functions that have out arguments; the boolean then indicates
whether the out arguments have been written. With "handle_sentinel_boolean_for", the
first return value is taken to be the sentinel boolean. If it is true, the rest of
the original return values will be returned, and otherwise an empty list will be
returned.
handle_sentinel_boolean_for => [
'Gtk3::TreeSelection::get_selected'
]
The function names refer to those after name corrections. Functions occuring in
"handle_sentinel_boolean_for" may also occur in "class_static_methods".
use_generic_signal_marshaller_for => [ [package1, signal1, [arg_converter1]], ... ]
Use an introspection-based generic signal marshaller for the signal "signal1" of type
"package1". If given, use the code reference "arg_converter1" to convert the
arguments that are passed to the signal handler. In contrast to Glib's normal signal
marshaller, the generic signal marshaller supports, among other things, pointer arrays
and out arguments.
reblessers => { package => \&reblesser, ... }
Tells G:O:I to invoke reblesser whenever a Perl object is created for an object of
type package. Currently, this only applies to boxed unions. The reblesser gets
passed the pre-created Perl object and needs to return the modified Perl object. For
example:
sub Gtk3::Gdk::Event::_rebless {
my ($event) = @_;
return bless $event, lookup_real_package_for ($event);
}
"Glib::Object::Introspection->invoke"
To invoke specific functions manually, you can use the low-level
"Glib::Object::Introspection->invoke".
Glib::Object::Introspection->invoke(
$basename, $namespace, $function, @args)
· $basename is the basename of a library, like 'Gtk'.
· $namespace refers to a namespace inside that library, like 'Window'. Use undef here
if you want to call a library-global function.
· $function is the name of the function you want to invoke. It can also refer to the
name of a constant.
· @args are the arguments that should be passed to the function. For a method, this
should include the invocant. For a constructor, this should include the package name.
"Glib::Object::Introspection->invoke" returns whatever the function being invoked returns.
Overrides
To override the behavior of a specific function or method, create an appropriately named
sub in the correct package and have it call "Glib::Object::Introspection->invoke". Say
you want to override "Gtk3::Window::list_toplevels", then do this:
sub Gtk3::Window::list_toplevels {
# ...do something...
my $ref = Glib::Object::Introspection->invoke (
'Gtk', 'Window', 'list_toplevels',
@_);
# ...do something...
return wantarray ? @$ref : $ref->[$#$ref];
}
The sub's name and package must be those after name corrections.
Converting a Perl variable to a GValue
If you need to marshal into a GValue, then Glib::Object::Introspection cannot do this
automatically because the type information is missing. If you do have this information in
your module, however, you can use Glib::Object::Introspection::GValueWrapper to do the
conversion. In the wrapper for a function that expects a GValue, do this:
...
my $type = ...; # somehow get the package name that
# corresponds to the correct GType
my $real_value =
Glib::Object::Introspection::GValueWrapper->new ($type, $value);
# now use Glib::Object::Introspection->invoke and
# substitute $real_value where you'd use $value
...
Handling extendable enumerations
If you need to handle extendable enumerations for which more than the pre-defined values
might be valid, then use "Glib::Object::Introspection->convert_enum_to_sv" and
"Glib::Object::Introspection->convert_sv_to_enum". They will raise an exception on
unknown values; catching it then allows you to implement fallback behavior.
Glib::Object::Introspection->convert_enum_to_sv (package, enum_value)
Glib::Object::Introspection->convert_sv_to_enum (package, sv)
SEE ALSO
perl-Glib: Glib
gobject-introspection: <http://live.gnome.org/GObjectIntrospection>
libffi: <http://sourceware.org/libffi/>
AUTHORS
Emmanuele Bassi <ebassi at linux intel com>
muppet <scott asofyet org>
Torsten Schönfeld <kaffeetisch at gmx de>
LICENSE
This library is free software; you can redistribute it and/or modify it under the terms of
the Lesser General Public License (LGPL). For more information, see
http://www.fsf.org/licenses/lgpl.txt