From portal.gmu.edu!hearst.acc.Virginia.EDU!caen!hookup!news.mathworks.com!news.alpha.net!uwm.edu!vixen.cso.uiuc.edu!howland.reston.ans.net!news.sprintlink.net!EU.net!sun4nl!news.nic.surfnet.nl!tuegate.tue.nl!krait.es.ele.tue.nl!tiggr Sun Mar 12 16:24:22 1995 Path: portal.gmu.edu!hearst.acc.Virginia.EDU!caen!hookup!news.mathworks.com!news.alpha.net!uwm.edu!vixen.cso.uiuc.edu!howland.reston.ans.net!news.sprintlink.net!EU.net!sun4nl!news.nic.surfnet.nl!tuegate.tue.nl!krait.es.ele.tue.nl!tiggr From: tiggr@es.ele.tue.nl (Tiggr) Newsgroups: comp.lang.objective-c,comp.answers,news.answers Subject: comp.lang.objective-c FAQ, part 1/3: Answer Supersedes: Followup-To: comp.lang.objective-c Date: 17 Feb 1995 17:00:04 GMT Organization: Eindhoven University of Technology, the Netherlands Lines: 692 Approved: news-answers-request@mit.edu Expires: 29 Mar 1995 17:00:02 GMT Message-ID: Reply-To: tiggr@es.ele.tue.nl (Tiggr) NNTP-Posting-Host: krait.es.ele.tue.nl Summary: This first part of the comp.lang.objective-c FAQ postings tries to answer all your Objective-C questions. Originator: tiggr@krait.es.ele.tue.nl Xref: portal.gmu.edu comp.lang.objective-c:1849 comp.answers:7061 news.answers:22121 Archive-name: Objective-C/answers Version: $Id: answers,v 3.5 1995/02/13 11:51:25 tiggr Exp $ Answers to FREQUENTLY ASKED QUESTIONS concerning Objective-C This is the first in a series of three informational postings concerning comp.lang.objective-c. This first part answers FAQs; the second part list available class libraries and the third part is a simple sample Objective-C program. This posting answers the following questions: 1 What is Objective-C 2 What is the difference between Objective-C and C++? 3 What exactly is it that makes Objective-C have `classes similar t Smalltalk', and what are the resulting capabilities of Objective-C? 4 What are the `nice features' of Objective-C? 5 What are some of the common problems of the language and how can I work around them? 6 What object encapsulation does Objective-C provide? 7 What are Protocols? 8 How can garbage collection be applied to Objective-C? 9 What is the difference between the NeXTSTEP, Stepstone and GNU CC versions of Objective-C? 10 What written information concerning Objective-C is available? 11 What kind of Objective-C support is provided by Stepstone? 12 What kind of Objective-C support is provided by NeXT? 13 What kind of Objective-C support is provided by GNU? 14 What kind of Objective-C support is provided by BPG. 15 What are the newsgroups to read or mailing lists to subscribe to in order to stay up-to-date on developments for GNU Objective-C? 16 Are there any FTP sites with Objective C code? Where? 17 For more information... (To find a question search on the question number starting a line.) 1 What is Objective-C? Objective-C is an object oriented computer programming language. It is a superset of ANSI C and provides classes and message passing similar t Smalltalk. Objective-C includes, when compared to C, a few more keywords and constructs, a short description of which follows. For a complete exampl of the application of the constructs, see part 3 of this FAQ `@interface' declares a new class. It indicates the name of the class, the name of its superclass, the protocols adhered to (see Q7), th layout of the instance variables (similar to the definition of a struct, but including encapsulation information (see Q19)) and declares th methods implemented by this class. A class' interface usually resides in a file called `.h'. `@implementation' defines a class. The implementation is no more than a collection of method definitions. Without an implementation, a class does not exist at run time. The implementation of a class usually resides in a file called `.m'. A `@category' is a named collection of method definitions which are added to an existing class. A category is not allowed to redefine a class' existing methods. Objective-C includes the predefined type `id' which stands for a pointer to some object. Thus, `id obj;' declares a pointer to an object. The actual class of the object being pointed to is almost irrelevant, since Objective-C does run-time type checking. `-message;' declares a method called `message'. The `-' indicates that the message can be sent to objects. A `+' instead indicates the messag can be sent to class objects. A method is similar to a function in that it has arguments and a return value. The default return type is `id'. If a method has nothing useful to return, it returns `self', which is pointer to the object to which the message was sent (similar to `this' in C++). [obj message], [obj message: arg1] and [obj message: arg1 with: arg2] are examples of sending a message to the object OBJ with 0, 1 and 2 arguments respectively. The name of the message is called the selector. In this example, the selectors are: `message', `message:' and `message:with:', respectively. 3 What is the difference between Objective-C and C++? C++ follows the Simula 67 school of OO programming, where Objective-C follows the Smalltalk school. In C++ the static type of an objec determine whether you can send it a message, in Objective-C the dynamic type determine it. The Simula 67 school is safer, in that more errors are detected at compile time. The Smalltalk school is more flexible, as some valid programs will execute correctly in Smalltalk, where they would be rejected by Simula 67. Stepstone's Objective-C allows you to chose between the dynamic and static binding, GNU and NeXT do not. ANSI C++ allows you to use dynamic binding, but discourages you from doing so. In many ways, the difference between C++ and Objective-C is more a question of mindset than technical barriers. Are you willing to offer some flexibility for some safety? Advocates for the Simula 67 school claims that a well designed program doesn't need the extra flexibility (a lie), while advocates for the Smalltalk school claims that the errors are no problem in practice (another lie). Pragmatic differences between Objective-C and C++ include: C++ has operator overloading. Some consider this to be `syntacti sugar', and it is, but it can be a quite handy bit of sugar. C++ has multiple inheritance. There are several ways to `get around' this in Objective-C (see below) The added syntax and semantics of C++ is huge, while Objective-C is C plus just a small number of new features. 3 What exactly is it that makes Objective-C have `classes similar to Smalltalk', and what are the resulting capabilities of Objective-C? Objective-C is as close to Smalltalk as a compiled language allows. Th following is a list of the features `taken' from Smalltalk: * Objective-C is compiled---Smalltalk is only partially compiled. Th current Objective-C implementations are all *much* faster than any Smalltalk. For example ParcPlace Smalltalk-80/4 is at least 3 times slower than both the GNU and NeXT Objective-C's. (This was measured using the Self/Smalltalk benchmark suite available by FTP from `self.stanford.edu:pub/Self-2.0.1'.) The big difference of course is that Objective-C does hybrid typing one can choose to represent a string as a `char *' or as an object, whereas in Smalltalk, everything is an object. This is a reason for Objective-C being faster. On the other hand, if every bit of information in an Objective-C program would be represented by a object, the program would probably run at a speed comparable to Smalltalk and it would suffer from not having optimization performed on the basic classes, like Smalltalk can do. * You may add or delete methods and classes at runtime. (On GNU and NeXT one can load new classes and categories. On Stepstone, which lacks categories, the only way to add methods is to load a subclass which then does a `+poseAs:' of the class to have methods added. This is less flexible, but it sort-of does the trick of just adding methods. * Much of the syntax, i.e. Smalltalk uses method names lik `a:method:name:', as does Objective-C. In Objective-C, the messag sending construct is enclosed in square brackets, like this: `[anObject aMessage: arg]' whereas Smalltalk uses something lik `anObject aMessage: arg'. * The basic class hierarchy, that is, having class `Object' in the ver top, and letting most other classes inherit from it. * Most method names in class object is the same. E.g. `respondsTo:'. What is called `doesNotUnderstand:' in Smalltalk is called `doesNotRecognize:' in Objective-C. * Smalltalk normally uses `doesNotUnderstand:' to implement forwarding, delegation, proxies etc. In Objective-C, these task are different: forwarding/delegation: `forward::' can be overridden to implement forwarding. On the NeXT, `forward::' is even use when passing to super. proxies: (Next) An instance of the NXProxy class forwards all methods and their arguments to the remote object via Mac messages. * Objective-C has meta classes mostly like Smalltalk * Objective-C does not have class variables like Smalltalk, but pool variables and globals are easily emulated via static variables. 4 What are the `nice features' of Objective-C? The possibility to load class definitions and method definition (which extend a class) at run time. Objects are dynamically typed: Full type information (name and type information of methods and instance variables and type information of method arguments) is available at run time. A prime example of application of this feature is `-loadNibSection:owner:' method of NeXTSTEP's Application class. Persistence [...] Remote objects [...]. Delegation and target/action protocols [...]. 5 What are some of the common problems of the language and how can I work around them There are some `common problems' There is no innate multiple inheritance (of course some see this as a benefit). To get around it you can create a compound class, i.e. a class with instance variables that are ids of other objects Instances can specifically redirect messages to any combination of the objects they are compounded of. (It isn't *that* much of a hassle and you have direct control over the inheritance logistics.) [Of course, this is not `getting around the problem of not having multiple inheritance', but just modeling your world slightly different in such a way that you don't need multiple inheritance.] Protocols address the absence of multiple inheritance (MI) to some extent: Technically, protocols are equivalent to MI for purely "abstract" classes (see the answer on `Protocols' below). [How does Delegation fit in here? Delegation is extending class' functionality in a way anticipated by the designer o that class, without the need for subclassing. One can, of course, be the delegate of several objects of differen classes. ] There are no class variables. You can get around this by defining a static variable in the implementation file, and defining access methods for it. This is actually a more desirable way of designing a class hierarchy, because subclasses shouldn't access superclass storage (this would cause the subclass to break if the superclass was reimplemented), and allows the subclass to override the storage (if the classes access all their own variables via methods). [The question remains what the exact syntax of class variables should be: Should a class object A be seen as an instance of its meta-class MA, which has a super class MB being the meta-class of A's super, B, and, as such, should A have separate instances of class variables defined for B? Or not?] 6 What object encapsulation does Objective-C provide? Object encapsulation can be discerned at two levels: encapsulation of instance variables and of methods. In Objective-C, the two are quit different Instance variables The keywords @public, @private and @protected are provided to secure instance variables from prying eyes to some extent. @public anyone can access any instance variable. @protected only methods belonging to this object' class or a subclass thereof have access to the instance variables. @private only methods of this class may access th instance variables. This excludes methods of a subclass. If not explicitly set, all instance variables are @protected. Note: Instance variable encapsulation is enforced at compile-time. At run-time, full typing information on all instance variables is available, which sort-of makes all variables @public again. This information is for instance used to do instance variable lookup by NeXTSTEP's `loadNibSection:owner:' method, making it completely safe. Methods: To the Objective-C runtime, all methods are @public. The programme can only show his/her intention of making specific methods no public by not advertising them in the class' interface. In addition, so-called private methods can be put in a category with special name, like `secret' or `private'. However, these tricks do not help much if the method is declared elsewhere, unless one reverts to indicating the object's type at compile time. And the runtime doesn't care about all this and an programmer can easily circumvent the tricks described. Thus, all methods really are always @public. 7 What are Protocols? Protocols are an addition to Objective-C that allows you to organize related methods into groups that form high-level behaviors. Protocols are currently available in NeXTSTEP (since 3.0) and GCC (since 2.4). Protocols address the MI issue. When you design an object with multipl inheritance, you usually don't want *all* the features of both A and B, you want feature set X from A and feature set Y from B. If those features are methods, then encapsulating X and Y in protocols allows yo to say exactly what you want in your new object. Furthermore, if someone changes objects A or B, that doesn't break your protocols or your new object. This does not address the question of new instance variables from A or B, only methods. Protocols allow you to get type-checking features without sacrificing dynamic binding. You can say "any object which implements the messages in Protocol Foo is OK for this use", which is usually what you want - you're constraining the functionality, not the implementation or the inheritance. Protocols give library builders a tool to identify sets of standard protocols, independent of the class hierarchy. Protocols provide language support for the reuse of design, whereas classes support the reuse of code. Well designed protocols can help users of an application framework when learning or designing new classes. Here is a simpl protocol definition for archiving objects: @protocol Archiving -read: (Stream *) stream; -write: (Stream *) stream @end Once defined, protocols can be referenced in a class interface as follows: /* MyClass inherits from Object and conforms to the Archiving protocol. */ @interface MyClass: Object @end Unlike copying methods to/from other class interfaces, any incompatible change made to the protocol will immediately be recognized by the compiler (the next time the class is compiled). Protocols also provide better type checking without compromising the flexibility of untyped, dynamically bound objects MyClass *obj1 = [MyClass new] // OK: obj1 conforms to the Archiving protocol id obj2 = obj1; // Error: obj1 does not conform to the TargetAction protocol. id obj3 = obj1; Another use of protocols is that you can declare an ID to conform to some protocol in order to help the compiler to resolve method nam conflicts @interface Foo: Object -(int) type; @en @protocol Bar -(const char *) type @end -blah1: d { id t = [d someMethod]; do_something_with ([t type]); } -blah2: d { id t = [d someMethod]; do_something_with ([t type]); } In this example, there are two kinds of the `-type' method. In the method `-blah1:', the compiler doesn't know what return type to expect from `[t type]', since it has seen both declarations of `-type'. In method `-blah2:', it knows that `t' conforms to the `Bar' protocol and thus that `t' implements the `-type' method returning a `const char *'. 8 How can garbage collection be applied to Objective-C? Currently, there are two implementations of garbage collection which can be used in Objective-C programs [that I'm aware of]. Both methods use a radically different approach. Garbage Collection in an Uncooperative Environmen This implements garbage collection of chunks of memory obtained through (its replacement of) malloc(3). It works for C, C++, Objective-C, etc. @article{bw88 title="Garbage Collection in an Uncooperative Environment", author="Hans J\"urgen Boehm and Mark Weiser", journal="Software Practice and Experience", pages=807-820,volume=18,number=9,month=sep,year=1988} It is available as `ftp://parcftp.xerox.com:/pub/gc/gc4.3.tar.gz'. Garbage Collection through Class Abstraction This implements garbage collection through class abstraction (and hence is Objective-C specific). Anything to be garbage collectible must be an object (instance of a subclass of a specific class) or have such an object for a wrapper. Available as `ftp://ftp.es.ele.tue.nl:/pub/tiggr/tobjc.tar.gz' Apart from the obvious radical difference, another difference currently is also noteworthy: The first method automatically protects objects pointed to from the stack, bss or data segments; the second doesn't. 9 What is the difference between the NeXTSTEP, Stepstone and GNU CC versions of Objective-C? NeXT extended Stepstone's definition of the language to include new constructs, such as protocols, which are touted to deal with som aspects of multiple inheritance. Stepstone supports static _binding_, whereas NeXTSTEP and GNU CC don't. All implementations do support static _typing_. Stepstone has a standard set of Foundation class libraries that work across all supported machines, including NeXTSTEP. NEXTSTEP comes with its own set of libraries (called `kits'). GNU libobjc.a currently only includes the `Object' class, though people are busy on a Real library (see part two of this FAQ (The ClassWare Listing) for details). The `Object' class of all implementations differ. NeXTSTEP and GNU CC support Categories, Stepstone doesn't NeXT has a native language debugger, Stepstone and GNU don't. [This is not really true, since NeXT's debugger is gdb, the GNU debugger, and their extensions are available though they haven't appeared in the official FSF distribution yet. Besides, debugging objc with a C debugger, like generic GDB, is quite acceptable.] NeXTSTEP (from version 3.0) and GCC (from version 2.4) support protocols and forward declarations of classes, Stepstone currently does not. 10 What written information concerning Objective-C is available? Books: Brad J. Cox, Andrew J. Novobilski: Object Oriented Programming: An Evolutionary Approach. Addison-Wesley Publishing Company, Reading, Massachusetts, 1991. ISBN: 0-201-54834-8. abstract: The first book on Objective-C, which actually is a book on object oriented system development using Objective-C. Lewis J. Pinson, Richard S. Wiener: Objective-C: Object Oriented Programming Techniques. Addison-Wesley Publishing Company, Reading, Massachusetts, 1991. ISBN 0-201-50828-1. abstract: Includes many examples, discusses both Stepstone's and NeXT's versions of Objective-C, and the differences between the two. Timothy Budd: An Introduction to Object-Oriented Programming Addison-Wesley Publishing Company, Reading, Massachusetts. ISBN 0-201-54709-0. abstract: An intro to the topic of OOP, as well as a comparison of C++, Objective-C, Smalltalk, and Object Pasca Simson L. Garfinkel, Michael K. Mahoney: NeXTSTEP Programming Step ONE: Object-Oriented Applications. TELOS/Springer-Verlag, 1993 (tel: (800)SPR-INGE). abstract: It's updated to discuss NeXTSTEP 3.0 features (Project Builder, new development environment) but doesn't discuss 3DKit or DBKit. NeXTSTEP Object Oriented Programming and the Objective C Language Addison-Wesley Publishing Company, Reading, Massachusetts, 1993 ISBN 0-201-63251-9. abstract: This book describes the Objective-C language as it is implemented for NeXTSTEP. While clearly targeted at NeXTSTEP, it is a good first-read to get to learn Objective-C Article `Why I need Objective-C', by Christopher Lozinski. Journal of Object-Oriented Programming (JOOP) September 1991. Contact info@bpg.com for a copy and subscription to the BPG newsletter. Abstract: This article discusses the differences between C++ and Objective-C in great detail and explains why Objective-C is a better object oriented language. `Concurrent Object-Oriented C (cooC)', by Rajiv Trehan et. al. ACM SIGPLAN Notices, Vol. 28, No 2, February 1993. Abstract: This article discusses cooC, a language based on the premise that an object not only provides a encapsulation boundary but should also form a process boundary. cooC is a superset of Objective-C. `Porting NEXTSTEP Applications to Microsoft Windows', by Christopher Lozinski. NEXTWORLD EXPO Conference Proceedings, San Francisco, CA, May 25-27, 1993. Updated version of the article available from the author. Contact info@bpg.com Abstract: This article describes how to develop Objective- applications for both Microsoft Windows an NEXTSTEP. GNU Documentatio The GNU project needs a free manual describing the Objective- language features. Because of its cause, GNU cannot include the non-free books in the GNU system, but the system needs to come wit documentation Anyone who can write good documentation, please think about giving it to the GNU project. Contact rms@gnu.ai.mit.edu 11 What kind of Objective-C support is provided by Stepstone? Compilers and runtime for: Apple Macintosh (running Mac Programmer Workshop), DEC Stations (ULTRIX), Data General AViiON (DG/UX), HP9000/300,400,700,800 (HP-UX), IBM RISC System/6000 (AIX), MIPS, NeXT, PC-AT (MS-DOS), PS/2 (AIX or OS/2), SCO/NCR UNIX SYS V, Sun 3, 4, SPARCstations (SunOS or Solaris), Silicon Graphics INDIGO and VAX(VMS). Other ports available by market demands or consulting services. ICpak101 Foundation Class Library is available on all the above. ICpak201 GUI Class Library is available on platforms that support XWindows, Motif, OpenWindows and SunView The Stepstone Corporation (203) 426-1875 - (800) BUY-OBJEct voice / (203) 270-0106 fa 75 Glen Road Sandy Hook, CT 06482 12 What kind of Objective-C support is provided by NeXT? The Objective-C compiler and libraries come bundled with the NEXTSTEP Developer CD. The compiler essentially is GNU CC. For information on the Kits which are part of NEXTSTEP, see th ClassWare Listing (part 2 of this FAQ). Products are NEXTSTEP 3.3 for NeXT, Intel and HP-PA Computers Enterprise Objects Framework 1. Portable Distributed Objects Release 2.0 NeXT Computer, Inc 900 Chesapeake Drive Redwood City, CA 94063 tel: 800 848 NEX fax: 415 780 2801 email: NeXTanswers@NeXT.COM www: http://www.next.com/ 13 What kind of Objective-C support is provided by GNU? GNU CC, since version 2, comes with an Objective-C compiler. The current distribution of GNU CC (version 2.6.3) includes an Objective- compiler and runtime library. The latter includes the `Object' class. Some people are working on GNU libraries, see part two of this FAQ (The ClassWare Listing) for details If you haven't switched to a GNU CC as recent as 2.4 yet, here's on reason to do so: The new runtime (as of 2.4) is more than 3 times as fast as the old runtime (pre 2.4) w.r.t. method invocation. Free Software Foundation 675 Massachusetts Avenu Cambridge, MA 0213 +1-617-876-3296 General questions about the GNU Project can be asked t gnu@prep.ai.mit.edu. GNU CC comes with an Objective-C compiler and runtime library which includes the Object class Most GNU software is packed using the new `gzip' compression program Source code is available on most sites distributing GNU software. For information on how to order GNU software on tape, floppy, o cd-rom, check the file etc/ORDERS in the GNU Emacs distribution or i GNUinfo/ORDERS on prep, or e-mail a request to: gnu@prep.ai.mit.edu By ordering your GNU software from the FSF, you help us continue t develop more free software. Media revenues are our primary source of support. Donations to FSF are deductible on US tax returns The following sites all carry mirrors of the GNU software at prep. Please try them before prep.ai.mit.edu! thanx -gnu@prep.ai.mit.edu ASIA: ftp.cs.titech.ac.jp, utsun.s.u-tokyo.ac.jp:/ftpsync/prep, cair.kaist.ac.kr:/pub/gnu, ftp.nectec.or.th:/pub/mirrors/gnu AUSTRALIA: archie.au:/gnu (archie.oz or archie.oz.au for ACSnet) AFRICA: ftp.sun.ac.za:/pub/gnu MIDDLE-EAST: ftp.technion.ac.il:/pub/unsupported/gnu EUROPE: irisa.irisa.fr:/pub/gnu, ftp.univ-lyon1.fr:pub/gnu, ftp.mcc.ac.uk, unix.hensa.ac.uk:/pub/uunet/systems/gnu ftp.denet.dk, src.doc.ic.ac.uk:/gnu, ftp.eunet.ch, nic.switch.ch:/mirror/gnu, ftp.informatik.rwth-aachen.de:/pub/gnu, ftp.informatik.tu-muenchen.de, ftp.win.tue.nl, ftp.funet.fi:/pub/gnu, ftp.stacken.kth.se, isy.liu.se, ftp.luth.se:/pub/unix/gnu, ftp.sunet.se:/pub/gnu, archive.eu.net SOUTH AMERICA: ftp.unicamp.br:/pub/gnu WESTERN CANADA: ftp.cs.ubc.ca:/mirror2/gnu USA: wuarchive.wustl.edu:/systems/gnu, labrea.stanford.edu, ftp.digex.net:/pub/gnu, ftp.kpc.com:/pub/mirror/gnu, f.ms.uky.edu:/pub3/gnu, jaguar.utah.edu:/gnustuff ftp.hawaii.edu:/mirrors/gnu, ftp.cs.widener.edu, vixen.cso.uiuc.edu:/gnu, mrcnext.cso.uiuc.edu:/pub/gnu, ftp.cs.columbia.edu:/archives/gnu/prep, col.hp.com:/mirrors/gnu, gatekeeper.dec.com:/pub/GNU, ftp.uu.net:/systems/gnu 14 What kind of Objective-C support is provided by BPG. BPG provides the Borland Extensions to Objective-C which allows the Objective-C translator to be used with the Borland Compiler, and make it easy to develop Objective-C application for Microsoft Windows. BPG provides the Smalltalk Interface to Objective-C which makes Objective-C objects look like Smalltalk Objects. It can be used to build Graphical User Interface on portable Objective-C objects, or to sell Objective-C libraries to Smalltalk developers. BPG provides the Objective-C Message Bus which sends Objective-C message across heterogeneous computer platforms. BPG has a library of objects for modelling Objective-C programs. A browser application has been built on this library. Other potential applications include adding class variables to Objective-C, adding runtime information about instance variables, and method argument types, generating object versions, and eventually building a browser/translator. Christopher Lozinski BPG 35032 Maidstone Court Newark, CA 9456 Tel: (510) 795-6086 fax: (510) 795-8077 email: info@bpg.com 15 What are the newsgroups to read or mailing lists to subscribe to in order to stay up-to-date on developments for GNU Objective-C? Read comp.lang.objective-c, which is bound to discuss current events. There is also a mailing list, gnu-objc@gnu.ai.mit.edu, discussing this very topic. To subscribe to this list, send a mail with your request to `gnu-objc-request@gnu.ai.mit.edu.' Furthermore, the various kits that are being developed each come with their own mailing list. See part 2 of this FAQ for more information. 16 Are there any FTP sites with Objective C code? Where? ftp.cs.rochester.edu:/pub/objc sonata.cc.purdue.edu (NEXTSTEP) cs.orst.edu (NEXTSTEP) ftp.stack.urc.tue.nl (NEXTSTEP) ftp.informatik.uni-muenchen.de ftp.informatik.uni-freiburg.d ccrma-ftp.stanford.edu (MusicKit ftp.cs.unl.edu:/pub/ObjC (sw && c.l.obj-c last few weeks) See also part 2 of this FAQ. 17 For more information... See part 2 of this FAQ, Objective-C/classes a.k.a. the ClassWare Listing, for an overview of available Objective-C classes and libraries. See part 3 of this FAQ, Objective-C/sample a.k.a. the Simple Sampl Program, for an example Objective-C program. The early version of this FAQ was compiled by Bill Shirley, with the aid of many people. The current version is being maintained by Tiggr, aided by a lot of people, including: Per Abrahamsen, Paul Burchard, Brad Cox, Christopher Lozinski, Mike Mahoney, Jon F. Rosen, Paul Sanchez, Lee Sailer Bill Shirley, Subrata Sircar, Ted Slupesky, Richard Stallman and Kersten Krab Thorup, A World Wide Web hypertext version of this FAQ is maintained by Brian Harvey (theharv@csld.ucr.edu) and can be found at: http://csld.ucr.edu/NeXTSTEP/objc_faq.html Any text in between `[' and `]' is a comment. Comments indicate `problems' with this FAQ, which should be solved. Send your suggestions, additions, bug reports, comments and fixes to `tiggr@es.ele.tue.nl'. The information in this file comes AS IS, WITHOUT ANY WARRANTY. You may use the information contained in this file or distribute this file, a long as you do not modify it, make money out of it or take the credits From portal.gmu.edu!hearst.acc.Virginia.EDU!caen!hookup!news.mathworks.com!news.alpha.net!uwm.edu!cs.utexas.edu!howland.reston.ans.net!EU.net!sun4nl!news.nic.surfnet.nl!tuegate.tue.nl!krait.es.ele.tue.nl!tiggr Sun Mar 12 16:24:22 199 Path: portal.gmu.edu!hearst.acc.Virginia.EDU!caen!hookup!news.mathworks.com!news.alpha.net!uwm.edu!cs.utexas.edu!howland.reston.ans.net!EU.net!sun4nl!news.nic.surfnet.nl!tuegate.tue.nl!krait.es.ele.tue.nl!tigg From: tiggr@es.ele.tue.nl (Tiggr Newsgroups: comp.lang.objective-c,comp.answers,news.answers Subject: comp.lang.objective-c FAQ, part 2/3: ClassWare Listing Supersedes: Followup-To: comp.lang.objective-c Date: 17 Feb 1995 17:00:06 GMT Organization: Eindhoven University of Technology, the Netherlands Lines: 960 Approved: news-answers-request@mit.edu Expires: 29 Mar 1995 17:00:02 GMT Message-ID: ASCIS DFG compiler), or at least interesting. I have been working on a new version which can handle messages sent to nil by setting something called the `objc_nil_class'. This mean that that particular class can receive messages while `self == nil', i.e. it is possible to make `[nil listp]' return YES. If you're interested, mail me for a copy (it is not good enough to be release through ftp yet). Contact Pieter J. `Tiggr' Schoenmakers email: tiggr@es.ele.tue.nl tel: +31 40 123484 fax: +31 40 128616 Public Domain Kits Various authors MiscKit [Abridged press release]. Update to Kit of Free Objective-C Objects Is Now Available PROVO, UT, Feb 9, 1995 -- A new maintenance release of the MiscKit has just been publically released. It contains many new objects and fixes all of the problems reported since th previous release. The MiscKit may be obtained via ftp to any o the following sites: ftp://ftp.cs.orst.edu/software/NeXT/sources/classes/MiscKit1.4.1.s.gnutar.gz ftp://ftp.et.byu.edu/next/misckit/MiscKit1.4.1.s.gnutar.gz ftp://ftp.informatik.uni-muenchen.de/pub/comp/platforms/next/Developer/objc/misckit/MiscKit1.4.1.s.gnutar.gz There are also accompanying binary packages built for various architectures available only at: ftp://ftp.et.byu.edu/next/misckit/MiscKit1.4.1.b.NIHS.gnutar.g ftp://ftp.et.byu.edu/next/misckit/MiscKit1.4.1.b.NI.gnutar.gz The byu site always has the most recent official MiscKit distribution available in /pub/next/misckit and older versions are archived in /pub/next/misckit/old. The MiscKit is an easy to install kit consisting of Objective- objects, Interface Builder palettes, bundles, and other useful programming resources. All the resources in the MiscKit hav been donated by various Internet personalities for the benefit of other NEXTSTEP programmers. Objects include data structures (string, tree, stack, queue, priority queue, linked list), interface widgets (find panel textfield, button and slider subclasses, clock and calendar views, icon wells, progress pie/bar), macros, other usefu objects (lock file, log file, time, stopwatch, serial port, colors, subprocess, remote subprocess, file), frameworks for building complex interfaces (MiscSwapKit, MiscInspectorKit InfoMenuKit) and even some useful example applications...plus much more To make the MiscKit more attractive to developers, use of the MiscKit resources is absolutely free of charge, no matter how the resources are used. Redistribution of the MiscKit is als encouraged. Many developers are reluctant to use objects which are under the GNU "Copyleft". As a result, the MiscKit has its own license which allows developers to reuse the code freely, even in commercial projects. Everything possible has been done to encourage the use of the MiscKit to speed development efforts. Any developer who has generally useful objects, palettes, or other programming resources and would like to donate them to th MiscKit effort is welcome to do so. Contact Don_Yacktman@byu.edu for information on how to prepare a MiscKit submission. By making a submission to the MiscKit, a developer can avoid the hassles of packaging up a formal distribution o their resources and in turn help add to a growing centralized pool of useful resources. Several MiscKit-based mailing lists are also available. The first list is for those who are interested in participating in the development of the MiscKit. Anyone who is interested i following the discussion should send mail t misckit-request@byu.edu to be placed on the list. Send mail t misckit@byu.edu to post messages to this list. The second MiscKit mailing list is for distributing announcements of new MiscKit releases. Anyone who would like to receive e-mail notification of new MiscKit releases should send mail to the MiscKit administrator, Don_Yacktman@byu.edu, and request to be placed on the MiscKit release list. Anyone on the developmen list already receives notification of new releases and shoul therefore not ask to be added to the release list. Two other lists are mentioned in the MiscKit's top level README.rtf file. The MiscKit has evolved from the DAYMiscKit and several objects released over the past few years by Don Yacktman and other USENET personalities. Contact For more information or to be placed on the MiscKit discussion list, contact the kit administrator, Don Yacktman, by sending e-mail to Don_Yacktman@byu.edu CCRMA MusicKit The Music Kit provides tools for designing music applications. These tools address three topics: music representation, performance, and synthesis (digital soun generation and processing). The Objective-C classes defined in the Music Kit fall neatly into these three areas. The design goal of the Music Kit is to combine the interactive gestural control of MIDI with the precise timbral control of MUSIC 5-type systems in an extensible, object-oriented environment. To this end, the Music Kit is capable of fully representing MIDI. The Music Kit accepts MIDI in and can send MIDI out through the two serial ports at the back of the computer. Nonetheless, the Music Kit isn't limited by the MIDI specification; for example, its resolution of frequency and amplitude is much finer than MIDI's highly quantized values. The Music Kit generates sounds by sending synthesis instructions to the DSP. The generality of the synthesis software far surpasses that of commercial synthesizers. While most synthesizers employ only one type of synthesis-the Yamaha DX-7 uses only frequency modulation, for example-the Music Kit can implement virtually any sound synthesis strategy. And since the synthesis engine (the DSP) and the control stream are brough together in a single high-performance computer, the Music Ki makes possible an unprecedented level of expressive control (from Documentation/MusicKit+DSP/General/SoundMusicDSP.rtfd MusicKit used to be supplied by NeXT as part of NeXTSTEP (pr 3.0). It is now maintained by CCRMA and available in tw packages: ftp://ccrma-ftp.stanford.edu/pub/NeXT/MusicKit_4.1.1.pkg.tar NI-fat Class library, header files, documentation programming examples, and a suite of applications (size = 13MB). ftp://ccrma-ftp.stanford.edu/pub/NeXT/MusicKitSource_4.1.1.pkg.tar Source of the MusicKit class library (size = 5MB). Contac email: musickit@ccrma.stanford.edu ADMINISTRATIVIA The information in this file comes AS IS, WITHOUT ANY WARRANTY. You ma use the information contained in this file or distribute this file, as long as you do not modify it, make money out of it or take the credits. All trademarks appearing in this file are owned by their respective owner. To increase the information content in this file, any indication to that effect is not present in the FAQ other than in this paragraph. The first version of this FAQ was written by Bill Shirly, helped by the feedback and information given to him by a lot of people. The curren version is maintained by Tiggr, supported by feedback from Glen Diener, Christopher Lozinski, Sean Luke and a lot of other people. Mail your bug reports, comments, suggestions and additions to tiggr@es.ele.tue.nl. A World Wide Web hypertext version of this FAQ is maintained by Brian Harvey (theharv@csld.ucr.edu) and can be found at: http://csld.ucr.edu/NeXTSTEP/objc_faq.html From portal.gmu.edu!hearst.acc.Virginia.EDU!caen!hookup!news.mathworks.com!news.alpha.net!uwm.edu!vixen.cso.uiuc.edu!howland.reston.ans.net!EU.net!sun4nl!news.nic.surfnet.nl!tuegate.tue.nl!krait.es.ele.tue.nl!tiggr Sun Mar 12 16:24:22 1995 Path: portal.gmu.edu!hearst.acc.Virginia.EDU!caen!hookup!news.mathworks.com!news.alpha.net!uwm.edu!vixen.cso.uiuc.edu!howland.reston.ans.net!EU.net!sun4nl!news.nic.surfnet.nl!tuegate.tue.nl!krait.es.ele.tue.nl!tiggr From: tiggr@es.ele.tue.nl (Tiggr) Newsgroups: comp.lang.objective-c,comp.answers,news.answer Subject: comp.lang.objective-c FAQ, part 3/3: A Sample Program Supersedes: Followup-To: comp.lang.objective-c Date: 17 Feb 1995 17:00:09 GMT Organization: Eindhoven University of Technology Lines: 948 Approved: news-answers-request@mit.edu Expires: 29 Mar 1995 17:00:02 GMT Message-ID: Reply-To: tiggr@es.ele.tue.nl (Tiggr NNTP-Posting-Host: krait.es.ele.tue.nl Summary: This third part of the comp.lang.objective-c FAQ postings presents a simple sample program written in Objective-C. Originator: tiggr@krait.es.ele.tue.nl Xref: portal.gmu.edu comp.lang.objective-c:1851 comp.answers:7063 news.answers:22123 Archive-name: Objective-C/sample Version: $Id: sample.preamble,v 1.1.1.1 1995/01/02 11:58:30 tiggr Exp $ A simple sample Objective-C progra This is the third part in a series of three informational posting concerning comp.lang.objective-c. This article presents a simple program written in Objective-C. The program consist of several files which ar contained in a shar file (see instructions below on how to unpack). [Note, from version 2.3 of this file, the sample has been changed in order to reduce the number of compiler warnings (down to 1, which is in there for explanatory purposes) and to reflect the use of `+alloc' and `-init' instead of `+new'. The early version of this FAQ was compiled by Bill Shirley, with the aid o many people. The current version is being maintained by Tiggr, aided by a lot of people, including Paul Sanchez and Bill Shirley. A World Wide Web hypertext version of this FAQ is maintained by Brian Harve (theharv@csld.ucr.edu) and can be found at http://csld.ucr.edu/NeXTSTEP/objc_faq.html Send your suggestions, additions, bug reports, comments and fixes to `tiggr@es.ele.tue.nl' #---------------------------------- cut here ---------------------------------- # This is a shell archive. Remove anything before this line, # then unpack it by saving it in a file and typing "sh file". # # Wrapped by Pieter Schoenmakers on Mon Jan 2 12:58:50 199 # # This archive contains: # objc-sampl # Existing files will not be overwritten. # Error checking via wc(1) will be performed. LANG=""; export LANG PATH=/bin:/usr/bin:$PATH; export PATH echo mkdir - objc-sample mkdir objc-sampl if test -f objc-sample/COPYRIGHT then echo Ok to overwrite existing file objc-sample/COPYRIGHT\ read answe case "$answer" in [yY]*) echo Proceeding;; *) echo Aborting; exit 1;; esac rm -f objc-sample/COPYRIGHT if test -f objc-sample/COPYRIGHT then echo Error: could not remove objc-sample/COPYRIGHT, aborting exit 1 fi fi echo x - objc-sample/COPYRIGHT cat >objc-sample/COPYRIGHT <<'@EOF This copyright notice applies to all source files distributed in the comp.lang.objective-c FAQ: `A Simple Sample Objective-C program'. Copyright (C) 1993 Paul J. Sanchez and Bill Shirley Copyright (C) 1994 Pieter J. Schoenmaker The `simple sample Objective-C program' is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. The `simple sample Objective-C program' is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNU Emacs; see the file COPYING. If not, write to the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. @EOF set `wc -lwc objc-sample/Char.h <<'@EOF' #import @interface Char: Object { int value } -init: (int) x; -report; @end @EOF set `wc -lwc objc-sample/Char.m <<'@EOF' #import #import "Char.h" @implementation Char { int value; } - init: (int) x { [super init]; // In case the parent class is doing // something special in its init... value = x; return self; } - report printf(" %c", value); return self; } @end @EOF set `wc -lwc objc-sample/Float.h <<'@EOF' #import @interface Float: Object { float value; } -initFloatValue: (float) x; -report; @end @EOF set `wc -lwc objc-sample/Float.m <<'@EOF' #import objc-sample/Makefile <<'@EOF' # This Makefile assumes you have GNU gcc 2.3 or better and a suitable # runtime library with object support. It also works on a NeXT # Don't know about Stepstone. .SUFFIXES: .o .m .m.o: $(CC) -c $(CFLAGS) $ # Use this on a NeX #CC= cc #LIBS= # Use this with GNU CC on a non-NeXT, # and avoid the GCC moaning on using #import. CC= gcc -Wno-import LIBS= -lobjc LDFLAGS= -L/usr/local/lib -L/usr/gnu/lib CFLAGS= -Wall - OFILES= main.o Node.o Queue.o Stack.o Float.o Char.o demo: $(OFILES $(CC) $(CFLAGS) $(LDFLAGS) -o demo $(OFILES) $(LIBS clean: rm -f $(OFILES) demo Char.o : Char.m Char.h Float.o : Float.m Float.h Node.o : Node.m Node.h Queue.o : Queue.m Queue.h Node.h Stack.o : Stack.m Stack.h Node.h main.o : main.m Queue.h Node.h Stack.h Float.h @EOF set `wc -lwc objc-sample/Node.h <<'@EOF' #import @interface Node : Object { id next; id data; } -init: anItem; // create a Node and store anItem in it -free; // free a Node and return the item in it -next; // report the id of the next node after this one -setNext: aNode; // make the next node be aNod @end @EOF set `wc -lwc objc-sample/Node.m <<'@EOF' #import #import "Node.h" @implementation Node: Object -init: anIte { self = [super init]; next = 0; data = anItem; return self; } -free { id tmp = data; [super free]; return tmp; } -next { return next; -setNext: aNode { next = aNode; return self; } @end @EOF set `wc -lwc objc-sample/Queue.h <<'@EOF' #import #import "Node.h" @interface Queue: Object { id head; id tail; unsigned qsize; } -empty; // clear out all contents of the Queue -put: anItem; // put anItem on the Queue -get; // return the item on top of the Queue -(unsigned int) size; // tell us the current size of the Queue @en @EOF set `wc -lwc objc-sample/Queue.m <<'@EOF' #import "Queue.h" @implementation Queue -empty { while([self size]) [[self get] free]; return self; } -put: anItem { if (tail) tail = [[tail setNext : [[Node alloc] init: anItem]] next]; else head = tail = [[Node alloc] init: anItem]; ++qsize return self; } -get { id contents; id old_head = head; head = [head next] contents = [old_head free]; if (--qsize == 0) tail = head return contents; } -(unsigned) size { return qsize; } @end @EOF set `wc -lwc objc-sample/README <<'@EOF This directory contains the complete code for the "Simple Sample Objective- program" described in the comp.lang.objective-c FAQ. If you have a suitable compiler, use the supplied Makefile. Otherwise, program output can be found in the file "output" You should probably read "main.m" first. It is very heavily annotated. Also note and read the file COPYRIGHT. @EOF set `wc -lwc objc-sample/Stack.h <<'@EOF' #import #import "Node.h" @interface Stack: Object { id stack; unsigned int stack_size; } -empty; // clear out all contents of the Stack -put: anItem; // put anItem on the Stack -get; // return the item on top of the Stack -(unsigned) size; // tell us the current size of the Stack @end @EOF set `wc -lwc objc-sample/Stack.m <<'@EOF' #import "Stack.h" @implementation Stack -empty { while([self size] [[self get] free]; return self; } -put: anItem { stack = [[[Node alloc] init: anItem] setNext : stack]; ++stack_size; return self; } -get { id contents; id old_stack = stack stack = [stack next]; contents = [old_stack free]; --stack_size; return contents; } -(unsigned) size { return stack_size } @end @EOF set `wc -lwc objc-sample/main.m <<'@EOF' /* main.m - comp.lang.objective-c simple sample Objective-C program. */ // This is a comment, just like the previous line. Everything to the right // of a double slash is ignored /* Classes are the one real extension which Objective-C adds to C. A class is a description of a collection of data, like a C structure, and th methods by which that data may be accessed or manipulated. Instances o a class are called objects, and methods are invoked by sending messages to either the class itself, to produce objects, or to those objects. The recipient of a message is called a "receiver". The form of a message is: [receiver method andMaybeSomeArguments] the receiver and method components are mandatory, as are the square brackets surrounding the message. Additional arguments may or may not b present, depending upon the method definition. Messages may appear anywhere a statement is allowed in C. The first thing we do is bring in some include files, as in C. On th NeXT, it is customary to use the "import" statement which guarantees tha the file isn't included more than once. Using GNU CC this is not all that nice sinds it generates a huge warning for every file being compiled. So, since it does not really matter, we'll stick to `#include'. */ #import #import #import "Queue.h" #import "Stack.h" /* That brought in class definitions for Objects, Queues, and Stacks. Th Object class is the basis for all other classes, which is why it gets brought in first. It provides basic functional behavior which is inherited by all derived classes. All user created classes normally have Object somewhere in their ancestry. Queue and Stack are classes of our own construction, and provide FIFO and LIFO storage capabilities, respectively. I'm not going to go into implementation details here. It's irrelevant how they work, all that is important is that they both respond to 'put:' and 'get'. If you want t inspect them, look into the Queue.m, Stack.m, Queue.h and Stack.h files. A simple Class definition follows. It inherits directly from the base class "Object". This gives it lots of nice properties, not the least of which is the ability to be referenced by any pointer of the generic object type "id". All objects can be pointed to by any id variable, and the default return type from methods is id. This allows messages to be embedded in other messages, either as receivers or arguments. An Int object allocates space for a single integer. The "report" message causes it to report its value. Everything between the @implementation and the @end is part of the class definition. Note - It is *highly* unusual to have a class implementation in your main program. Since the object is fully defined before it gets used, no interface description is required. There is nothing illegal about doing things this way, but it is so unusual that the compiler will produce warning for this class. The Int class implementation is here solely for expository purposes. */ @implementation Int: Object // Int is derived from Object { int value; // This is the data portion. Like a struct. } /* The following are the method definitions. A `+' prefix means it is a factory method, i.e., how to manufacture instances of the class. The body of the method is between braces, like a C function. This class doesn't define any factory methods. It relies on the +alloc method defined in class Object. For examples of factory methods, look at the +new method defined in the Stack or Queue implementations. Self is a special variable, which refers to the object currently being manipulated. Super refers to the parent class of self. The following method asks the parent class (Object) to hand us a new instance, which becomes self. Then we update the instance variables and return a pointe to the new object. It is standard for methods that do not need to return any special valu to instead return self. This allows for a nested syntax of method calls. The "-" in front of init means that it's an instance method, i.e., something a particular object should respond to. */ -init: (int) i { /* We're overriding the `-init' of our superclass, but we ad functionality instead of replacing it. Therefore, first call th `-init' of our superclass. */ [super init]; value = i; return self; -report { printf ("%4d", value) return self; } @end /* We have implemented Float and Char classes more traditionally, using separate files for the interface (.h) and implementation (.m). The Float and Char objects are like the Int object, but with the obvious difference that they work with floats and characters. We include the interface definitions at this point. */ #import "Float.h" #import "Char.h" /* If you inspect those files, note polymorphism -- methods have same names as in the Int class. */ int main (void { /* First create instances of "Stack" and "Queue" data structures. */ id queue = [[Queue alloc] init]; id stack = [[Stack alloc] init] int i, reply fprintf (stderr, "Include the Char class in the demo? (y/n): "); /* Anything not matching `y.*' means no. */ reply = getchar (); for (i = 5; i > -6; --i) { /* Depending on which version of the demo we're running, we alternately put Ints and Floats onto the queue and stack, or Ints, Floats, and Chars. * if (reply == 'y') { /* If I is odd we put an Int on the queue and a Char on the stack. If I is even we put an Char on the queue and a Float on the stack. Since there is more than one method `-init:' and since `+alloc' returns a plain, typeless, `id', the compiler doesn't know the type of the object returned by alloc. An explicit cast (i.e. static type indication) ensures that th compiler knows which `init:' is invoked---the one accepting a char or the other one accepting an int. Another solution, which avoids the static type indication, is to put typing information on the method in the method's name. This is done for the Float class. */ id my_char = [(Char *) [Char alloc] init: 'm' + i]; if (i & 1) { [queue put: [(Int *) [Int alloc] init: i]]; [stack put: my_char]; } else [queue put: my_char]; [stack put: [[Float alloc] initFloatValue: i]]; } } else { /* If I is odd we put an Int on the queue and a Float on the stack. If I is even we put a Float on the queue and an Int on the stack. */ [queue put: ((i & 1) ? [(Int *) [Int alloc] init: i] : [[Float alloc] initFloatValue: i])]; [stack put: ((i & 1) ? [[Float alloc] initFloatValue: i] : [(Int*) [Int alloc] init: i])] } } while ([queue size] && [stack size]) { /* The following illustrates run-time binding. Will report be invoked for a Float object or an Int object? Did the user elect for Char objects at run time? We don't know ahead of time, but with run-time binding and polymorphism it works properly. The burden is on the class implementer rather than the class user. Note that the following lines remain unchanged, whether we are using the Char class or not. The queue and stack hand us the next object, it reports itself regardless of its type, and then it frees itself. */ printf ("queue:"); [[[queue get] report] free] printf (", stack:"); [[[stack get] report] free]; putchar('\n'); } return 0; } @EOF set `wc -lwc objc-sample/output <<'@EOF' Output from demo, excluding Char class: Include the Char class in the demo? (y/n): n queue: 5, stack:-5.0 queue: 4.0, stack: -4 queue: 3, stack:-3.0 queue: 2.0, stack: -2 queue: 1, stack:-1. queue: 0.0, stack: 0 queue: -1, stack: 1. queue:-2.0, stack: 2 queue: -3, stack: 3.0 queue:-4.0, stack: 4 queue: -5, stack: 5.0 Output from demo, including Char class: Include the Char class in the demo? (y/n): y queue: 5, stack: h queue: q, stack:-4.0 queue: 3, stack: j queue: o, stack:-2.0 queue: 1, stack: l queue: m, stack: 0.0 queue: -1, stack: n queue: k, stack: 2. queue: -3, stack: p queue: i, stack: 4.0 queue: -5, stack: @EOF set `wc -lwc