Glib(3) User Contributed Perl Documentation Glib(3)NAMEGlib - Perl wrappers for the GLib utility and Object libraries
SYNOPSIS
use Glib;
ABSTRACT
This module provides perl access to GLib and GLib's GObject libraries.
GLib is a portability and utility library; GObject provides a generic
type system with inheritance and a powerful signal system. Together
these libraries are used as the foundation for many of the libraries
that make up the Gnome environment, and are used in many unrelated
projects.
DESCRIPTION
This wrapper attempts to provide a perlish interface while remaining as
true as possible to the underlying C API, so that any reference
materials you can find on using GLib may still apply to using the
libraries from perl. This module also provides facilities for creating
wrappers for other GObject-based libraries. The "SEE ALSO" section
contains pointers to all sorts of good information.
PERL VERSUS C
GLib provides to C programs many of the same facilities Perl offers
natively. Where GLib's functionality overlaps Perl's, Perl's is
favored. Some concepts have been eliminated entirely, as Perl is a
higher-level language than C. In other instances we've had to add or
change APIs to make sense in Perl. Here's a quick run-down:
Perl Already Does That
The GLib types GList (a doubly-linked list), GSList (singly-linked
list), GHashTable, GArray, etc have all been replaced by native Perl
datatypes. In fact, many functions which take GLists or arrays simply
accept lists on the Perl stack. For the most part, GIOChannels are no
more functional than Perl file handles, so you won't see any
GIOChannels. GClosures are not visible at the Perl level, because Perl
code references do the same thing. Just about any function taking
either a C function pointer or a GClosure will accept a code reference
in Perl. (In fact, you can probably get away with just a subroutine
name in many spots, provided you aren't using strict subs.)
Don't Worry About That
Some concepts have been eliminated; you need never worry about
reference-counting on GObjects or having to free GBoxed structures.
Perl is a garbage-collected language, and we've put a lot of work into
making the bindings take care of memory for you in a way that feels
natural to a Perl developer. You won't see GValues in Perl (that's
just a C structure with Perl scalar envy, anyway).
This Is Now That
Other GLib concepts have been converted to an analogous Perl concept.
The GType id will never be seen in Perl, as the package name serves
that purpose. Several packages corresponding to the GTypes of the
fundamental types have been registered for you:
G_TYPE_STRING Glib::String
G_TYPE_INT Glib::Int
G_TYPE_UINT Glib::UInt
G_TYPE_DOUBLE Glib::Double
G_TYPE_BOOLEAN Glib::Boolean
The remaining fundamentals (char/uchar, short, float, etc) are also
registered so that we can properly interact with properties of C
objects, but perl really only uses ints, uints, and doubles. Oh, and
we created a GBoxed type for Perl scalars so you can use scalars where
any boxed type would be allowed (e.g. GtkTreeModel columns):
Glib::Scalar
Functions that can return false and set a GError in C raise an
exception in Perl, using an exception object based on the GError for
$@; see Glib::Error. Trapping exceptions in signals is a sticky issue,
so they get their own section; see EXCEPTIONS.
Enumerations and flags are treated as strings and arrays of strings,
respectively. GLib provides a way to register nicknames for
enumeration values, and the Perl bindings use these nicknames for the
real values, so that we never have to deal with numbers in Perl. This
can get a little cumbersome for bitfields, but it's very nice when you
forget a flag value, as the bindings will tell you what values are
accepted when you pass something invalid. Also, the bindings consider
the - and _ characters to be equivalent, so that signal and property
names can be properly stringified by the => operator. For example, the
following are equivalent:
# property foo-matic of type FooType, using the
# value FOO_SOMETHING_COOL. its nickname would be
# 'something-cool'. you may use either the full
# name or the nickname when supplying values to perl.
$object->set ('foo-matic', 'FOO_SOMETHING_COOL');
$object->set ('foo_matic', 'something_cool');
$object->set (foo_matic => 'something-cool');
Beware that Perl will always return to you the nickname form, with the
dash.
Flags have some additional magic abilities in the form of overloaded
operators:
+ or | union of two flagsets ("add")
- difference of two flagsets ("sub", "remove")
* or & intersection of two bitsets ("and")
/ or ^ symmetric difference ("xor", you will rarely need this)
>= contains-operator ("is the left set a superset of the right set?")
== equality
In addition, flags in boolean context indicate whether they are empty
or not, which allows you to write common operations naturally:
$widget->set_events ($widget->get_events - "motion_notify_mask");
$widget->set_events ($widget->get_events - ["motion_notify_mask",
"button_press_mask"]);
# shift pressed (both work, it's a matter of taste)
if ($event->state >= "shift-mask") { ...
if ($event->state * "shift-mask") { ...
# either shift OR control pressed?
if ($event->state * ["shift-mask", "control-mask"]) { ...
# both shift AND control pressed?
if ($event->state >= ["shift-mask", "control-mask"]) { ...
In general, "+" and "-" work as expected to add or remove flags. To
test whether any bits are set in a mask, you use "$mask * ...", and to
test whether all bits are set in a mask, you use "$mask >= ...".
When dereferenced as an array @$flags or "$flags->[...]", you can
access the flag values directly as strings (but you are not allowed to
modify the array), and when stringified "$flags" a flags value will
output a human-readable version of its contents.
It's All the Same
For the most part, the remaining bits of GLib are unchanged. GMainLoop
is now Glib::MainLoop, GObject is now Glib::Object, GBoxed is now
Glib::Boxed, etc.
FILENAMES, URIS AND ENCODINGS
Perl knows two datatypes, unicode text and binary bytes. Filenames on a
system that doesn't use a utf-8 locale are often stored in a local
encoding ("binary bytes"). Gtk+ and descendants, however, internally
work in unicode most of the time, so when feeding a filename into a
GLib/Gtk+ function that expects a filename, you first need to convert
it from the local encoding to unicode.
This involves some elaborate guessing, which perl currently avoids, but
GLib and Gtk+ do. As an exception, some Gtk+ functions want a filename
in local encoding, but the perl interface usually works around this by
automatically converting it for you.
In short: Everything should be in unicode on the perl level.
The following functions expose the conversion algorithm that GLib uses.
These functions are only necessary when you want to use perl functions
to manage filenames returned by a GLib/Gtk+ function, or when you feed
filenames into GLib/Gtk+ functions that have their source outside your
program (e.g. commandline arguments, readdir results etc.).
These functions are available as exports by request (see "Exports"),
and also support method invocation syntax for pathological consistency
with the OO syntax of the rest of the bindings.
$filename = filename_to_unicode $filename_in_local_encoding
$filename = Glib->filename_to_unicode ($filename_in_local_encoding)
Convert a perl string that supposedly contains a filename in local
encoding into a filename represented as unicode, the same way that
GLib does it internally.
Example:
$gtkfilesel->set_filename (filename_to_unicode $ARGV[1]);
This function will croak() if the conversion cannot be made, e.g.,
because the utf-8 is invalid.
$filename_in_local_encoding = filename_from_unicode $filename
$filename_in_local_encoding = Glib->filename_from_unicode ($filename)
Converts a perl string containing a filename into a filename in the
local encoding in the same way GLib does it.
Example:
open MY, "<", filename_from_unicode $gtkfilesel->get_filename;
Other functions for converting URIs are currently missing. Also, it
might be useful to know that perl currently has no policy at all
regarding filename issues, if your scalar happens to be in utf-8
internally it will use utf-8, if it happens to be stored as bytes, it
will use it as-is.
When dealing with filenames that you need to display, there is a much
easier way, as of Glib 1.120 and glib 2.6.0:
$uft8_string = filename_display_name ($filename)
$uft8_string = filename_display_basename ($filename)
Given a $filename in filename encoding, return the filename, or
just the file's basename, in utf-8. Unlike the other functions
described above, this one is guaranteed to return valid utf-8, but
the conversion is not necessarily reversible. These functions are
intended to be used for failsafe display of filenames, for example
in gtk+ labels.
Since gtk+ 2.6, Glib 1.12
EXCEPTIONS
The C language doesn't support exceptions; GLib is a C library, and of
course doesn't support exceptions either. In Perl, we use die and eval
to raise and trap exceptions as a rather common practice. So, the
bindings have to work a little black magic behind the scenes to keep
GLib from exploding when the Perl program uses exceptions.
Unfortunately, a little of this magic has to leak out to where you can
see it at the Perl level.
Signal and event handlers are run in an eval context; if an exception
occurs in such a handler and you don't catch it, Perl will report that
an error occurred, and then go on about its business like nothing
happened.
You may register subroutines as exception handlers, to be called when
such an exception is trapped. Another function removes them for you.
$tag = Glib->install_exception_handler (\&my_handler);
Glib->remove_exception_handler ($tag);
The exception handler will get a fresh copy of the $@ of the offending
exception on the argument stack, and is expected to return non-zero if
the handler is to remain installed. If it returns false, the handler
will be removed.
sub my_handler {
if ($_[0] =~ m/ftang quisinart/) {
clean_up_after_ftang ();
}
1; # live to fight another day
}
You can register as many handlers as you like; they will all run
independently.
An important thing to remember is that exceptions do not cross main
loops. In fact, exceptions are completely distinct from main loops.
If you need to quit a main loop when an exception occurs, install a
handler that quits the main loop, but also ask yourself if you are
using exceptions for flow control or exception handling.
LOG MESSAGES
GLib's g_log function provides a flexible mechanism for reporting
messages, and most GLib-based C libraries use this mechanism for
warnings, assertions, critical messages, etc. The Perl bindings offer
a mechanism for routing these messages through Perl's native system,
warn() and die(). Extensions should register the log domains they wrap
for this to happen fluidly. [FIXME say more here]
64 BIT INTEGERS
Since perl's integer data type can only hold 32 bit values on all 32
bit machines and even on some 64 bit machines, Glib converts 64 bit
integers to and from strings if necessary. These strings can then be
used to feed one of the various big integer modules. Make sure you
don't let your strings get into numerical context before passing them
into a Glib function because in this case, perl will convert the number
to scientific notation which at this point is not understood by Glib's
converters.
Here is an overview of what big integer modules are available. First
of all, there's Math::BigInt. It has everything you will ever need,
but its pure-Perl implementation is also rather slow. There are
multiple ways around this, though.
Math::BigInt::FastCalc
Math::BigInt::FastCalc can help avoid the glacial speed of vanilla
Math::BigInt::Calc. Recent versions of Math::BigInt will
automatically use Math::BigInt::FastCalc in place of
Math::BigInt::Calc when available. Other options include
Math::BigInt::GMP or Math::BigInt::Pari, which however have much
larger dependencies.
Math::BigInt::Lite
Then there's Math::BigInt::Lite, which uses native Perl integer
operations as long as Perl integers have sufficient range, and
upgrades itself to Math::BigInt when Perl integers would overflow.
This must be used in place of Math::BigInt.
bigint / bignum / bigfloat
Finally, there's the bigint/bignum/bigfloat pragmata, which
automatically load the corresponding Math:: modules and which will
autobox constants. bignum/bigint will automatically use
Math::BigInt::Lite if it's available.
Exports
For the most part, gtk2-perl avoids exporting things. Nothing is
exported by default, but some functions and constants in Glib are
available by request; you can also get all of them with the export tag
"all".
Tag: constants
TRUE
FALSE
G_PRIORITY_HIGH
G_PRIORITY_DEFAULT
G_PRIORITY_HIGH_IDLE
G_PRIORITY_DEFAULT_IDLE
G_PRIORITY_LOW
G_PARAM_READWRITE
Tag: functions
filename_from_unicode
filename_to_unicode
filename_from_uri
filename_to_uri
filename_display_basename
filename_display_name
SEE ALSO
Glib::Object::Subclass explains how to create your own gobject
subclasses in Perl.
Glib::index lists the automatically-generated API reference for the
various packages in Glib.
This module is the basis for the Gtk2 module, so most of the references
you'll be able to find about this one are tied to that one. The perl
interface aims to be very simply related to the C API, so see the C API
reference documentation:
GLib - http://developer.gnome.org/doc/API/2.0/glib/
GObject - http://developer.gnome.org/doc/API/2.0/gobject/
This module serves as the foundation for any module which needs to bind
GLib-based C libraries to perl.
Glib::devel - Binding developer's overview of Glib's internals
Glib::xsapi - internal API reference for GPerl
Glib::ParseXSDoc - extract API docs from xs sources.
Glib::GenPod - turn the output of Glib::ParseXSDoc into POD
Glib::MakeHelper - Makefile.PL utilities for Glib-based extensions
Yet another document, available separately, ties it all together:
http://gtk2-perl.sourceforge.net/doc/binding_howto.pod.html
For gtk2-perl itself, see its website at
gtk2-perl - http://gtk2-perl.sourceforge.net/
A mailing list exists for discussion of using gtk2-perl and related
modules. Archives and subscription information are available at
http://lists.gnome.org/.
AUTHORS
muppet, <scott at asofyet dot org>, who borrowed heavily from the work
of GA~Xran Thyni, <gthyni at kirra dot net> and Guillaume Cottenceau
<gc at mandrakesoft dot com> on the first gtk2-perl module, and from
the sourcecode of the original gtk-perl and pygtk projects. Marc
Lehmann <pcg at goof dot com> did lots of great work on the magic of
making Glib::Object wrapper and subclassing work like they should.
Ross McFarland <rwmcfa1 at neces dot com> wrote quite a bit of the
documentation generation tools. Torsten Schoenfeld <kaffeetisch at web
dot de> contributed little patches and tests here and there.
COPYRIGHT AND LICENSE
Copyright 2003-2006 by muppet and the gtk2-perl team
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
perl v5.10.0 2006-09-04 Glib(3)