Maintained by Andrew McCallum mccallum@gnu.ai.mit.edu, with contributions by Pascal Forget pascal@wsc.com, Scott Christley scottc@net-community.com, and Randy Chapman chapman@u.washington.edu.
Last updated 26 March 1996. The most up-to-date version of this FAQ is available at ftp://ftp.cs.rochester.edu/pub/u/mccallum/gnustep-base. Please send corrections to mccallum@gnu.ai.mit.edu.
The intended audience of this FAQ is future and present code developers for GNUstep. This FAQ serves a purpose complementary to the GNUstep WWW pages--since it is written and maintained directly by those writing code for GNUstep, it emphasizes (although not exclusively): (1) technical details and organization, (2) the functionality is coded and working now. This FAQ is intended to provide a succinct document in which to find GNUstep information without hype.
GNUstep is the Free Software Foundation's effort to implement NeXT Software Inc.'s OpenStep Standard. The project is not finished, however some components are useable now.
The GNUstep project consists of the following sub-projects:
More detailed information about each of these sub-projects can be found in their own sections below.
There are several projects related to GNUstep that are not officially part of the GNU project and GNUstep, but may become so in the future. These include: the `G3DKit' project, (contact Thomas Engle tsengel@cip.informatik.uni-erlangen.de); an application library based on OpenGL, (contact Georg Tuparev Tuparev@EMBL-Heidelberg.de); and `ProjectCenter', a source code management and development environment, (contact unknown). If you know of others, please contact the FAQ maintainer.
The initial target platforms for GNUstep are Linux and other UN*X's. There has been some OS/2 WARP work, but I have not seen any ongoing work on this platform yet, (contact McCallum if you are interested).
OpenStep is an Application Programming Interface (API) for creating applications using the Objective C language. It was published by NeXT Computer Inc. in 1994.
OpenStep consists of three parts: the `FoundationKit', a library of non-graphical objects; the `AppKit', a library of objects usful in creating graphical applications; and `DisplayPostscript', an interface for drawing to the screen using the PostScript graphics language.
You can obtain a copy of the OpenStep standard in
For the sake of being social and getting to know each other, here is a list of the folks who are currently, actively contributing GNUstep code. The list includes a brief descriptions of each person's background and involvement in the GNUstep coding efforts.
There are many others who have made significant contributions to GNUstep, but who are not currently contributing code, (such as Kresten Thorup krab@next.com and Paul Kunz paul_kunz@slac.stanford.edu). For more information about GNUstep history, see the GNUstep WWW pages.
There are also several others who have contributed individual classes to GNUstep, but who are not actively contributing to general GNUstep work. This list is not intended to be a complete list of GNUstep code contributors; that information is available in each of the GNUstep code packages.
There are also other code developers who are writing Objective C code related to GNUstep, but for projects that are not officially part of the GNU project and GNUstep. We hope that some of these projects will join the GNU project and GNUstep in the future.
Please send corrections to the FAQ maintainer.
There is a WWW site at http://www.GNUstep.org, (and its mirror http://www.NMR.EMBL-Heidelberg.DE/GNUstep, that contains many useful pointers. The technical information in this FAQ may be more up to date than the WWW pages since this FAQ is maintained directly by the people who are developing GNUstep code.
There are several mailing lists:
To join, send mail to discussion-request@gnustep.org.
To join, send mail to webmasters-request@gnustep.org.
To join, send mail to g3dkit@gnustep.org.
The Base Library is about 85 percent done. Significant useful work can already be done using the library. The GUI library is about 25 percent done. It is going through a major transition at the moment to coordinate work from multiple developers, DisplayPostscript, and the non-OpenStep objcX library into a single package that will be made available to the public. The DisplayPostscript and drawing support is also in transition.
More detailed information about the state of each of the sub-projects can be found below.
With free software, you should never, ever, believe promises about when a project will be finished. ...However, that said: there are certain GNUstep developers that are counting on having useful Base and GUI libraries working by the end of Summer 1996.
The short answer is: On whichever platforms volunteers offer port it! The main target platforms is free operating systems, namely Linux and the Hurd. Much of the code is OS-independent, and should port quite easily to various UNIX-like OS's. There has been interest in a port to Linux on the Apple Macintosh, but I have not heard of any developers.
At least one of the current active developers is also working with WindowsNT. There has been some interest in an OS/2 port, but I've seen few code contributions for OS/2.
If you have a specific piece of functionality that you would like to contribute, or if you would like to ask for suggestions about what coding work you can do to help, contact the GNUstep Chief Maintainer, Andrew McCallum mccallum@gnu.ai.mit.edu.
More detailed inforation about each of the GNUstep sub-projects can be found below.
The Objective C Runtime Library provides C functions and data structures required to execute an Objective C program. An introduction to the Objective C Language is provided at http://www.next.com/Pubs/Documents/OPENSTEP/ObjectiveC/objctoc.htm. The Frequently Asked Questions list for news://comp.lang.objective-c can be found at ??.
The GNU Objective C Runtime Library offers everything NeXT's runtime does, including Categories, Protocols, `+poseAs:', thread-safety, class initialization on demand, delayed loading of classes, and initialization of static instances (such as @""-style string objects).
It also has several improvements over NeXT's implementation:
GNU's Objective C Runtime library has been stable and useable since 1993. Enhancements continue to be made.
GCC contains the source for the GNU Objective C compiler and runtime library. It can be obtained from ftp://prep.ai.mit.edu/pub/gnu, or any other mirror of the GNU archives. As far as I know, the GNU Objective C Runtime runs on all, platforms on which GCC runs.
GCC version 2.7.2 does not contain the thread-safe features, but the next version of GCC will. A patch for thread-safe features is provided with the latest developer snaphots of the GNUstep Base Library. There are currently thread-safe backends for DEC OSF/1, Solaris, IRIX, and WindowsNT. Volunteers are solicited for writing additional back-ends, especially one for Linux.
The GNUstep Base Library is a library of general-purpose, non-graphical Objective C objects. For example, it includes classes for strings, collections, byte streams, typed coders, invocations, notifications, notification dispatchers, times, network ports, remote object messaging support, event loops and random number generators.
It provides functionality that aims to implement the `FoundationKit' portion of the OpenStep standard. In many cases, the `NS*' classes are implemented as wrappers around more featureful GNU classes.
There is more (although perhaps out-of-date) information available at the GNUstep Base Library homepage at http://www.cs.rochester.edu/u/mccallum/gnustep-base.
It is about 85 percent of the way to having all the OpenStep classes. Significant useful work can already be done using the library since the missing 15 percent are the less-often-used classes, such as NSByteStore. Over 60,000 lines of code have already been written.
The following OpenStep classes and class clusters are pretty much done and usable: NSArchiver, NSArray, NSAssertionHandler, NSAutoreleasePool, NSBitmapCharSet, NSBundle, NSCharacterSet, NSCoder, NSCountedSet, NSData, NSDate, NSDictionary, NSEnumerator, NSException, NSInvocation, NSLock, NSMethodSignature, NSNotification, NSNotificationCenter, NSNumber, NSObject, NSProcessInfo, NSRunLoop, NSSet, NSString, NSThread, NSTimeZone, NSTimer, NSValue.
Most of the C functions are also implemented, including NSHashTable and NSMaptable.
A GNU implementation of Distributed Object works. However, the wrappers for creating the NSConnection, NSDistantObject, NSProxy wrappers have not yet been made.
The following classes are unstarted or unusable: NSBTreeBlock, NSBTreeCursor, NSByteStore, NSByteStoreFile, NSCalendarDate, NSDeserializer, NSScanner, NSSerializer, NSUserDefaults.
It contains several enhancements:
All of them respond to a new method called `-invokeWithObject:' that is useful for enumerations.
OpenStep notifications must be method selectors sent to objects. GNUstep notifications can invoke an Invocation instead, thus taking advantage of the flexbility and context-holding capability of Invocation objects.
Unlike OpenStep, the Base Library also has additional collection classes for heaps, stacks, queues, trees and linked lists. There is also a rich variety of enumeration methods based on invocations.
I'm not sure how OpenStep's archiving system implements forward
references, (that is, calls to `encodeConditionalObject:' for which
the object argument has not yet been encoded, but will be encoded
later.) According to its restricted interface, NeXT's implementation
must either (1) make two passes through all the -encodeWithCoder:
methods of the objects to be encoded, or (2) not handle forward
references with `-encodeConditionalObject:', only backward
references. GNU's archiving system, on the other hand, implements
forward references efficiently, without making two passes. It does this
by using an object decoding method (`-decodeObjectAt:..') that
back-patches id-pointers when the conditionally encoded objects
are found in the coded stream.
GNU Distributed Objects has many of the features of other distributed objects implementations, but, since it is free software, it can be ported to platforms for which other distributed objects implementations are not available.
If you are interested in having it ported to a new platform, or if you have any questions about it, please contact Andrew McCallum, mccallum@gnu.ai.mit.edu.
The distributed object support classes are Connection, Proxy, ConnectedCoder, Port, TcpPort, UdpPort, and MachPort. Of the various Port backend's, currently only the the TcpPort is in working order.
[NOTE: The GNU distributed object facilities have the same ease-of-use as NeXT's; be warned, however, that they are not compatible with each other. They have different class heirarchies, different instance variables, different method names, different implementation strategies and different network message formats. You cannot communicate with a NeXT NXConnection using a GNU Connection.
Here are some differences between GNU distributed objects and NeXT's distributed objects: NXConnection creates NXProxy objects for local objects as well as remote objects; GNU Connection doesn't need and doesn't create proxies for local objects. NXProxy asks it's remote target for the method encoding types and caches the results; GNU Proxy gets the types directly from the local GNU "typed selector" mechanism and has no need for querying the remote target or caching encoding types. The NXProxy for the remote root object always has name 0 and, once set, you cannot change the root object of a NXConnection; the GNU Proxy for the remote root object has a target address value just like all other Proxy's, and you can change the root object as many times as you like. See the "lacking-capabilities" list below for a partial list of things that NXConnection can do that GNU Connection cannot.]
Here is a partial list of what the current distributed objects system can do:
Here is a partial list of what the current distributed objects system does not yet do:
(This FAQ does not describe the OpenStep standard classes, because a detailed description of those can be found in the OpenStep documentation.)
Here are some of the public GNU classes. See the source header files for more information.
The collection class heirarchy:
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Collection Root all the collection classes (abstract)
Set Unordered collection, no duplicates
Bag Unordered collection, may have duplicates
KeyedCollection Contents accessible by object key (abstract)
Dictionary Concrete implementation
MappedCollection One collection maps into another
IndexedCollection Contents accessible by integer (abstract)
BinaryTree Basic, sorted binary tree
RBTree Red-Black tree, sorted, more balanced
SplayTree Splay operation keeps tree balanced
OrderedCollection Can insert at arbitrary index (abstract)
Array Basic array
Queue First in, first out
Stack First in, last out
GapArray Efficient handle middle insert and delete
LinkedList More efficient than arrays for some ops
Strings (as in Smalltalk, part of the collection class heirarchy):
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ConstantString Root of string classes, chars not changable
String contents can be changed
*CString Strings based on 1-byte characters
Writing/reading bytes, C-type variables, and connected groups of objects:
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Stream Source and Destination for stream of bytes
StdioStream Stream based on FILE* (files, pipes, etc)
MemoryStream Stream based on memory buffer
CStream Write/Read C-type variables on stream
TextCStream use human-readable format
BinaryCStream use compact machine independent format
RawCStream use even more compact machine depedent format
Coder Write/Read groups of objects on CStream
Encoder Writing
Archiver for files
ConnectedEncoder for distributed objects
Decoder Reading
Unarchiver for files
ConnectedDecoder for distributed objects
Holding code to be run on request:
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Invocation Contains code that can be run
ArgframeInvocation based on gcc __builtin_apply()
MethodInvocation invokes a method on an object
ObjectMethodInvocation the method takes at least one object arg
ObjectFunctionInvocation calls a function with type (id(*)(id))
VoidFunctionInvocation calls a functions with type (void(*)())
Posting information about happenings:
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Notification for posting information others may want
NotificationRequest a record of an observers request
NotificationInvocation will be posted by invoking an Invocation
NotificationPerformer will be posted by -perform:withObject
NotificationDispatcher distributes Notification's among requestors
Distributed Objects Support:
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Connection between two machines on which messages sent
Proxy Representative of a remote object
Port A mailbox for packets
InPort for receiving packets
OutPort for sending packets
Tcp*Port based on TCP/IP
Udp*Port based on UDP/IP
Mach*Port based on Mach ports
Packet holds data and reply port
The most recently released "official" version can be obtained from ftp://prep.ai.mit.edu.
The most recently released alpha version can be obtained from ftp://alpha.gnu.ai.mit.edu.
The most recent developer's snapshot can be obtained from ftp://ftp.cs.rochester.edu/pub/u/mccallum/gnustep-base. These releases are there for exchange between active GNUstep coders, and for curious code-readers, not for naive users; read the README.first file in the FTP directory.
The GNUstep GUI Library is a library of objects useful for writing graphical applications. For example, it includes classes for drawing and manipulating graphics objects on the screen: windows, menus, buttons, sliders, text fields, and events. There are also many peripheral classes that offer operating-system-independent interfaces to images, cursors, colors, fonts, pasteboards, printing. There are also workspace support classes such as data links, open/save panels, context-dependent help, spell checking.
It provides functionality that aims to implement the `AppKit' portion of the OpenStep standard. However the implementation has been written to take advantage of GNUstep enhancements wherever possible.
The GNUstep GUI Library is divided into a front- and back-end. The front-end contains the majority of implementation, but leaves out the low-level drawing and event code. A back-end can override whatever methods necessary in order to implement low-level drawing event receiving. Different back-ends will make GNUstep available on various platforms. The default GNU back-end will run on top of X Windows and the DisplayGhostScript Server. Other back-ends could allow GNUstep to run on OpenGL, OS/2, and WIN32 graphics/event platforms. Much work will be saved by this clean separation between front- and back-end, because it allows different platforms to share the large amount of front-end code.
The front-end does not specify what mechanism to use in order to "plug in" the back-end--that is the back-end implementor's choice. At least two backends will use `+poseAs:' method, for example, running `[XDPSWindow poseAs: [NSWindow class]]'. Using `+poseAs:' is more flexible than using Categories because it allows the the back-end implementor to choose what to override in the front-end, instead of having the interface between front- and back-end fixed by the front-end.
A number of classes in the front-end are complete or almost complete; these include: NSActionCell, NSButtonCell, NSButton, NSCell, NSControl, NSEvent, NSFont, NSResponder, and NSSlider.
Other classes are complete enough to use, but still require some major additions before being considered almost complete: NSApplication, NSBox, NSColor, NSFontManager, NSMenu, NSMenuCell, NSPopUpButton, NSSliderCell, NSText, NSTextField, NSTextFieldCell, NSView, and NSWindow.
All remaining classes have stub implementations.
It is not yet publically available. When it is available you will be able to find it in ftp://alpha.gnu.ai.mit.edu/gnu.
Interface Modeller, in its simplest form, is an application for visually constructing and prototyping graphical user interfaces. At a more abstract level, it is a tool for connecting instances of Objective C classes to create a graph of objects; this graph is a model of an executable program that Interface Modeller can save to a file to be loaded and executed later outside of Interface Modeller.
It is in the specification stage; no code has been written yet. The current specifications are available through the GNUstep WWW pages.
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