PerlObjCBridge(3) User Contributed Perl Documentation PerlObjCBridge(3)
NAME
PerlObjCBridge.pm - Bridges Perl and Objective-C runtimes
SYNOPSIS
use Foundation;
$s1 = NSString->stringWithCString_("Hello ");
$s2 = NSString->alloc()->initWithCString_("World");
$s3 = $s1->stringByAppendingString_($s2);
printf "%s\n", $s3->cString();
SUMMARY
The PerlObjCBridge module supports creating and messaging Objective-C
objects from Perl programs, allowing Cocoa objects in Apple Computer's
Mac OS X to be directly manipulated from Perl. In addition, Perl
objects can be messaged from Objective-C, making it possible for Perl
objects to function as Cocoa delegates and as targets of notifications
and other Cocoa call-back messages. Perl programs can take advantage of
Cocoa's Distributed Objects mechanism to support messaging between Perl
objects and Objective-C objects (or other Perl objects) in different
address spaces, possibly on different machines.
LIMITATION
This version of PerlObjCBridge does not directly support writing GUI
Cocoa applications in Perl. Consult
http://www.sourceforge.net/projects/camelbones for a freeware package
that supports GUI Perl/Cocoa apps.
DESCRIPTION
Using PerlObjCBridge, Perl programs can reference Objective-C objects
in a manner similar to references to native Perl objects. The
Objective-C objects must inherit from the NSObject root class in the
Mac OS X Foundation framework (which is true for Cocoa objects). In
Objective-C an object is accessed via an object identifier that is
implemented as a pointer to a structure containing the object's
instance data. PerlObjCBridge represents an Objective-C object as a
Perl reference to a scalar value that contains the Objective-C ID. For
example, if an Objective-C object has an ID with value 0x12345678, then
PerlObjCBridge represents that object as a reference to a scalar with
value 0x12345678. The Perl reference is "blessed" into a Perl class
that has the same name as the Objective-C class. The Perl inheritance
mechanism is then used to route any messages sent to the object from
Perl through the PerlObjCBridge extension module and ultimately to the
Objective-C object. The return values of the Objective-C messages are
similarly routed back through the bridge where they are converted into
Perl return values.
It is also possible to use Perl objects in places where Cocoa methods
normally take Objective-C arguments. For example, one can register Perl
objects to receive NSNotifications, in which case the perl objects
provide the notification handling methods that are asynchronously
messaged by NSNotificationCenter when interesting events occur. As
another example, a Perl object can be registered as a server object via
NSConnection, after which Objective-C or Perl objects in other address
spaces can send messages to the server object via the Distributed
Objects mechanism. In these examples an Objective-C proxy object is
created by PerlObjCBridge that gets passed to Objective-C methods, and
that forwards messages from Objective-C to the Perl object.
MESSAGING
Ordinary Perl "object->method(argument-list)" syntax is used to send
messages to Objective-C objects. The ':' character that delimits
arguments in Objective-C is illegal in Perl method names, so
underscores are used instead. An method that is invoked in Objective-C
as:
[anObject arg1:x arg2:y];
can be invoked from Perl using something like:
$anObject->arg1_arg2_($x, $y);
Contrast the following Objective-C code fragment with its Perl analogue
in the synopsis at the top of this man page:
#import <Foundation/Foundation.h>
NSString *s1 = [NSString stringWithCString:"Hello "];
NSString *s2 = [[NSString alloc] initWithCString:"World"];
NSString *s3 = [s1 stringByAppendingString:s2];
printf("%s\n", [s3 cString]);
To send a message to an Objective-C class, one uses the syntactic form
ClassName->method(...args...). For example, one can send the
"defaultManager" message to the NSFileManager class as follows:
$defMgr = NSFileManager->defaultManager();
An important special case of a class method is a "factory" method that
constructs a new instance of a class:
$array = NSMutableArray->array();
$string = NSString->stringWithCString_("Hi there");
The NSString factory method illustrates how PerlObjCBridge passes Perl
strings to Objective-C as char *'s.
To send a message to an Objective-C object, one uses the syntactic form
$object->method(...args...). If $array is a reference to an
NSMutableArray then one can add the NSString referenced by $string by
sending $array the "addObject:" message:
$array->addObject_($string);
Message sends can be chained from left to right:
$hostName = NSProcessInfo->processInfo()->hostName();
In the above example, the object returned by
NSProcessInfo->processInfo() is in turn sent the hostName message.
USING COCOA FRAMEWORKS
PerlObjCBridge automatically generates a bridge module for the
Foundation framework that is included with the Cocoa environment in Mac
OS X. This bridge module is created when PerlObjCBridge is built. The
bridge module for a framework causes that framework to be dynamically
loaded into the Perl program's address space. In addition Perl packages
are created for each of the Objective-C classes in the framework so
that the Objective-C classes exist in the Perl name space.
To access a framework from Perl "use" its bridge module. For example,
to access Foundation objects do:
use Foundation;
DISTRIBUTED MESSAGING
Perl objects can send messages to other objects (Perl or Cocoa) in
different address spaces by using Cocoa's Distributed Objects (DO)
mechanism. This makes it easy to create distributed systems (such as
client/server systems) that mix Perl and Cocoa programs. It also makes
it easy to create a pure Perl distributed system, where Perl objects in
different address spaces communicate via Cocoa DO.
Here is a complete example of a distributed client/server system, where
the client and server objects are written in Perl but communicate by
means of DO. The system consists of a Perl client program, a Perl
server program, and a Perl XSUB module that provides the glue between
the Perl programs and DO. The XSUB module is initially created by
running the following command:
h2xs -A -n AddSystem
An AddSystem directory is created with these files:
ppport.h
lib/AddSystem.pm
AddSystem.xs
Makefile.PL
README
t/AddSystem.t
Changes
MANIFEST
Edit the Makefile.PL DEFINE entry to add the -ObjC flag:
'DEFINE' => '-ObjC', # e.g., '-DHAVE_SOMETHING'
Modify the contents of AddSystem.pm to contain:
package AddSystem;
@ISA = qw(Exporter DynaLoader);
@EXPORT = qw( );
$VERSION = '1.0';
bootstrap AddSystem $VERSION;
use Foundation;
1;
and modify AddSystem.xs to have the contents:
#include <mach-o/dyld.h>
#include "EXTERN.h"
#include "perl.h"
#include "XSUB.h"
#ifdef Move
#undef Move
#endif Move
#ifdef DEBUG
#undef DEBUG
#endif DEBUG
#ifdef I_POLL
#undef I_POLL
#endif I_POLL
#import <Foundation/Foundation.h>
@interface AddClient : NSObject
@end
@implementation AddClient
- (int)firstNumber { return 0; }
- (int)secondNumber { return 0; }
@end
@interface AddServer: NSObject
@end
@implementation AddServer
- (int)addNumbersForClient:(NSObject *)client { return 0; }
@end
MODULE = AddSystem PACKAGE = AddSystem
AddSystem.xs defines "dummy" AddClient and AddServer Objective-C
classes that implement the methods that the Perl client and server will
provide. These dummy Objective-C classes are needed in this case
because there would otherwise not be enough information for the DO
runtime system to determine the numbers, types, and sizes of the method
arguments and return values. These dummy Objective-C implementations
are usually only needed when DO is being used and the Perl program does
not link against any libraries that contain objects that already
implement the methods. The actual method bodies are irrelevant and can
be trivially defined to return 0 or NULL. In the case of methods that
return void, the dummy methods can have empty bodies.
After modifying Makefile.PL, AddSystem.pm, and AddSystem.xs, execute
the following commands (as root or as an admin user):
perl Makefile.PL
make install
Now add two Perl programs to the AddSystem directory. The first program
is addServer:
#!/usr/bin/perl
use AddSystem;
package AddServer;
@ISA = qw(PerlObjCBridge);
@EXPORT = qw( );
PerlObjCBridge::preloadSelectors('AddClient');
sub new
{
my $class = shift;
my $self = {};
bless $self, $class;
return $self;
}
sub addNumbersForClient_
{
my($self, $client) = @_;
my $first = $client->firstNumber();
my $second = $client->secondNumber();
return int($first + $second);
}
$server = new AddServer;
$connection = NSConnection->defaultConnection();
$connection->setRootObject_($server);
$connection->registerName_(NSString->stringWithCString_("AddServer"));
NSRunLoop->currentRunLoop()->run();
Make sure that the line "#!/usr/bin/perl" does not contain leading
whitespace.
The line:
use AddSystem;
causes addServer to load the AddSystem XSUB module, which in turn loads
the dummy AddClient and AddServer Objective-C classes, thus making them
available to the DO runtime system. The lines:
package AddServer;
@ISA = qw(PerlObjCBridge);
@EXPORT = qw( );
cause the AddServer package to inherit from PerlObjCBridge. As a
consequence, messages to and from AddServer objects will be routed
through PerlObjCBridge.
The line:
PerlObjCBridge::preloadSelectors('AddClient');
instructs PerlObjCBridge to pre-cache all method selectors for the
Objective-C class AddClient. By doing this, PerlObjCBridge is "primed"
with the information needed to send messages to objects of class
AddClient.
After a standard "new" constructor method, there is a
addNumbersForClient_ method that provides the service vended by the
AddServer class. The method name "addNumbersForClient_" corresponds to
the Objective-C selector "addNumbersForClient:", which has a dummy
implementation in AddSystem.xs. In addition to the standard $self
argument, addNumbersForClient_ takes a second argument $client which is
a reference to the invoking client object. The client object is then
sent the messages "firstNumber" and "secondNumber", each of which
returns an integer. The server adds the two numbers and returns the
result.
The lines:
$server = new AddServer;
$connection = NSConnection->defaultConnection();
$connection->setRootObject_($server);
$connection->registerName_(NSString->stringWithCString_("AddServer"));
create a new AddServer object and set it as the root object of a DO
connection, registered with the name "AddServer". Clients can then look
up the name "AddServer" to connect to this object.
The final line:
NSRunLoop->currentRunLoop()->run();
puts addServer into a event loop, waiting for incoming connections from
clients.
The second program, addClient, consists of:
#!/usr/bin/perl
use AddSystem;
package AddClient;
@ISA = qw(PerlObjCBridge);
@EXPORT = qw( );
PerlObjCBridge::preloadSelectors('AddServer');
sub new
{
my $class = shift;
my $self = {};
bless $self, $class;
$self{'firstNumber'} = shift;
$self{'secondNumber'} = shift;
return $self;
}
sub firstNumber
{
my($self) = @_;
return $self{'firstNumber'};
}
sub secondNumber
{
my($self) = @_;
return $self{'secondNumber'};
}
die "usage: perlClient <firstNumber> <secondNumber>\n" unless @ARGV == 2;
# create client
$client = new AddClient (@ARGV);
# create connection to server
$name = NSString->stringWithCString_("AddServer");
$server = NSConnection->rootProxyForConnectionWithRegisteredName_host_($name, 0);
if (!$server or !$$server) {
print "Can't get server\n";
exit(1);
}
$server->retain();
printf "%d\n", $server->addNumbersForClient_($client);
Make sure that the line "#!/usr/bin/perl" does not contain leading
whitespace.
The AddClient methods "firstNumber" and "secondNumber" implement the
call-back methods invoked by the AddServer. The lines:
$name = NSString->stringWithCString_("AddServer");
$server = NSConnection->rootProxyForConnectionWithRegisteredName_host_($name, 0);
if (!$server or !$$server) {
print "Can't get server\n";
exit(1);
}
$server->retain();
results in $server being assigned a DO "proxy" object for the AddServer
object in the addServer program. Any messages sent by the client will
by forwarded by the DO proxy to the actual AddServer object in the
addServer address space.
The final line:
printf "%d\n", $server->addNumbersForClient_($client);
invokes the AddServer object with a reference to the client object. The
control flow that results is:
addClient sends "addNumbersForClient:" to addServer
addServer sends "firstNumber" to addClient
addClient returns first number
addServer sends "secondNumber" to addClient
addClient returns second number
addServer returns sum of first and second number
To execute these programs, first make sure addServer and addClient are
executable:
chmod +x addServer addClient
Next run the server in one shell:
addServer
then the client in another shell:
addClient 1 2
3
AUTOMATIC STRING CONVERSION
For convenience, PerlObjCBridge automatically converts Perl strings
into NSString Objective-C objects when an NSObject is expected as the
argument to an Objective-C method. For example, suppose an Objective-C
dictionary is created:
$dict = NSMutableDictionary->dictionary();
The dictionary method "setObject:forKey:" expects the key argument to
be an NSString and the value argument to be any NSObject. The following
automatically converts both "aKey" and "aValue" to NSStrings and then
inserts the pair into the dictionary:
$dict->setObject_forKey_("aValue", "aKey");
The value can be retrieved as follows, where "aKey" is again
automatically converted to an NSString:
$value = $dict->objectForKey_("aKey");
printf "value is %s\n", $value->cString();
Note that the return value assigned to $value is a reference to an
NSString and is not automatically converted to a Perl string. The
automatic conversions occur only from Perl strings to NSStrings for
Objective-C method arguments. NSStrings return values are not
automatically converted to Perl strings.
Automatic conversion also occurs when a Perl string is passed as an
argument to a method that expects an Objective-C selector. For example,
the "performSelector:" message can be sent to any NSObject. The
argument to the "performSelector:" message must be an Objective-C
selector. In Objective-C, one can copy an existing NSString
"origString" by asking it to perform the "copy" selector:
copy = [origString performSelector:@selector(copy)];
This is equivalent to:
copy = [origString copy];
In Perl the selector form can be executed as:
$copy = $origString->performSelector_("copy");
In this case the Perl string "copy" is automatically converted to an
Objective-C selector.
NIL ARGUMENTS AND RETURN VALUES
It is sometimes necessary to pass the Objective-C object ID "nil" (a
null pointer) as an argument to an Objective-C method. Since
PerlObjCBridge represents Objective-C ID's as Perl references, strictly
speaking the Perl value 0 is not a legal representation for Objective-
C's nil because it is a simple scalar, not a reference. However, for
convenience, when an argument to an Objective-C method is expected to
be an object ID and the value 0 is passed from Perl, PerlObjCBridge
coerces the 0 value to a reference to a zero-valued scalar and the
Objective-C method receives nil for that argument. In the following
example, the Objective-c method "arg1:optionalArg:" would receive nil
as its second argument.
MyClass->arg1_optionalArg_($obj, 0);
The special value "undef" can also be used:
MyClass->arg1_optionalArg_($obj, undef);
When an Objective-C method returns nil, the corresponding Perl return
value is a reference to a zero-valued scalar. This return value can
subsequently be passed as an argument to an Objective-C method. In the
following example, if "aMethod" returns nil then "arg1:optionalArg:"
would receive nil as its second argument:
MyClass->arg1_optionalArg_($obj, YourClass->aMethod());
To determine whether an Objective-C method returned nil one should test
both the Perl reference and its referent. The referent will be zero-
valued when the Objective-C method returned nil, but it is also
possible for the reference itself to be undefined (for example, when
the method raised an NSException, as discussed below). The following
example illustrates the use of an Objective-C NSEnumerator object to
print the elements of an NSArray. In Objective-C, the enumerator
returns nil after the last object in the array has been enumerated. In
the Perl loop, both the reference $obj and the referent $$obj are
tested in the loop condition. Under normal circumstances looping ends
when $$obj becomes zero-valued, indicating the enumerator returned nil.
$enumerator = $array->objectEnumerator();
while ($obj = $enumerator->nextObject() and $$obj) {
printf "%s\n", $obj->description()->cString();
}
EXCEPTION HANDLING
NSExceptions that are raised as a result of messages sent by Perl
programs to Objective-C objects are dealt with as follows.
PerlObjCBridge has a built-in NSException handler that writes the
message selector, the class of the target object, and the NSException
name, reason, and userInfo to standard error. By default, the built-in
NSException handler then dies with a message. The function
PerlObjCBridge::setDieOnExceptions() can be used to control the latter
behavior. Invoking setDieOnExceptions() with an argument of 0 will
cause the built-in exception handler to issue a warning and return
without dying, whereas a non-zero argument (or no argument) will cause
the built-in exception handler to die. In the case where the built-in
exception handler returns with a warning, the original message that
caused the exception returns undef.
Alternatively, the Perl program can set its own exception handler by
calling PerlObjCBridge::setNSExceptionHandler() with a single argument
that must be a reference to a Perl function that acts as the exception
handler. The Perl program can get a reference to the current exception
handler by calling PerlObjCBridge::getNSExceptionHandler(). If a user-
defined exception handler is set and an NSException is raised then the
user-defined handler will be called with five string arguments: (1) the
Objective-C selector for the message that induced the NSException, (2)
the class name of the object to which the message was sent, and (3,4,5)
the NSException name, reason, and userInfo (the latter represented as
the string [userInfo description]). If the user-defined exception
handler returns, then the original message returns undef. When a user-
defined exception handler is set, it is up to the handler to decide
whether the program exits or continues when NSExceptions are raised
(i.e., when a user-defined exception handler is set the function
setDieOnExceptions() has no effect).
The example below stores the original exception handler, sets a new
exception handler, provokes an NSException by attempting to set a
dictionary entry with a nil key and a nil value, and then restores the
original exception handler.
sub myHandler
{
my($sel, $pkg, $name, $reason, $userInfo) = @_;
print "NSException raised!\n";
print "selector: $selector\n";
print "package: $package\n";
print "name: $name\n";
print "reason: $reason\n";
print "userInfo: $userInfo\n";
}
$oldHandler = PerlObjCBridge::getNSExceptionHandler();
PerlObjCBridge::setNSExceptionHandler(\&myHandler);
$dict = NSMutableDictionary->dictionary();
$dict->setObject_forKey_(0, 0);
PerlObjCBridge::setNSExceptionHandler($oldHandler);
This results in myHandler printing the output:
NSException raised!
selector: setObject:forKey:
target class: NSCFDictionary
name: NSInvalidArgumentException
reason: *** -[NSCFDictionary setObject:forKey:]: attempt to insert nil key
userInfo:
LARGE NUMERIC VALUES
PerlObjCBridge assumes no Perl support for 64-bit integers. When an
Objective-C method has a 64-bit integer return type (i.e., long long or
unsigned long long) and the result of invoking that method is a return
value that is too large (i.e., >= 2^^31) or too small (<= -(2^^31)) to
be represented in Perl as a signed integer then the value is returned
as a Perl double. Similarly, when a parameter to an Objective-C method
is a long long or unsigned long long then the type of the Perl argument
value is examined. If the argument value is a Perl integer then its
value is passed directly to the Objective-C method in long long or
unsigned long long form (coercing in the unsigned case). Otherwise if
the argument value is a Perl double then it is coerced to the
appropriate long long or unsigned long long form before it is passed to
the method.
Similar considerations apply to 32-bit unsigned longs and unsigned
ints. When an Objective-C method has a 32-bit unsigned long or unsigned
int return type and the result of invoking that method is a return
value that is too large (>= 2^^31) to be represented in Perl as a
signed integer then the value is returned as a Perl double. When a
parameter to an Objective-C method is a 32-bit unsigned long or
unsigned int then the Perl int or float argument is simply coerced to
the unsigned long or int. This can of course have unpleasant
consequences if the Perl argument is negative or larger than 2^^32.
CONTROL FUNCTIONS
Calling PerlObjCBridge::setTracing() with a non-zero argument (or no
argument) will cause PerlObjCBridge to log diagnostic messages as it
executes. Calling setTracing() with an argument of zero turns the
diagnostics off.
Calling PerlObjCBridge::setDieOnErrors() with a non-zero argument (or
no argument) will cause PerlObjCBridge to die with a warning message
whenever there is an error during the sending of an Objective-C message
(this is the default behavior). Calling setDieOnErrors() with an
argument of zero allows the program to print a warning message but not
die after such an error.
BUGS AND LIMITATIONS
PerlObjCBridge should take advantage of Perl support for 64-bit
integers if available. Feel free to fix this.
When structs are passed by value, sometimes pointers embedded in the
structs get mangled. It is better to pass structs by reference if they
contain embedded pointers.
Varargs-style messaging is not supported. This is unfortunate, but it's
due to the lack of varargs support in NSInvocation and
NSMethodSignature. Fix that and it should be easy to support varargs
messaging in PerlObjCBridge.
Access to functions, variables, and other non-object-oriented
constructs exported by libraries containing Objective-C is not
currently supported. It seems dubious that those things are exported as
C-level constructs to begin with, when they could/should be Objective-C
class methods. One possible workaround is to create an XSUB that
provides Objective-C "covers" for these items. For example, if a
library exports a variable:
extern int GreatBigFoo;
then an XSUB with a cover might define:
@interface Covers: NSObject
+ (int)GreatBigFoo;
@end
@implementation Covers
+ (int)GreatBigFoo
{
return GreatBigFoo;
}
@end
Then the value of the variable could be accessed in Perl:
$gbf = Covers::GreatBigFoo();
SEE ALSO
perl(1). Mac OS X: /Developer/Documentation/Cocoa/ObjectiveC Mac OS X:
/Developer/Documentation/Cocoa/Reference/Foundation
perl v5.10.0 2008-06-13 PerlObjCBridge(3)
Mac OS X 10.6 - Generated Thu Sep 17 20:14:37 CDT 2009