MacTech 1 to 12/MacTech-vol-1-12.toast/Reference/FAQs on CD/comp.lang.obj-C FAQ (1⁄3) ans

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Newsgroups: comp.lang.objective-c,comp.answers,news.answers
From: [e-mail] (Tiggr)
Subject: comp.lang.objective-c FAQ, part 1/3: Answers
Summary: This first part of the comp.lang.objective-c FAQ postings
    tries to answer all your Objective-C questions.
Reply-To: [e-mail] (Tiggr)
Followup-To: comp.lang.objective-c
Organization: Eindhoven University of Technology, the Netherlands
Approved: [e-mail]
Keywords:

Archive-name: Objective-C/answers
Version: $Id: answers,v 3.36 1997/01/31 14:16:17 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 lists
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 to
     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  How do I debug Objective-C using a non-NeXT gdb?
 11  I get this `Floating exception'...
 12  Why am I lectured by gcc about `#import'?
 13  Did NeXT buy Stepstone?  [NO!]
 14  What written information concerning Objective-C is available?
 15  What kind of Objective-C support is provided by Stepstone?
 16  What kind of Objective-C support is provided by NeXT?
 17  What kind of Objective-C support is provided by GNU?
 18  Is Objective-C supported on <my favourite platform>?
 19  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?
 20  Are there any FTP sites with Objective C code?  Where?
 21  If there any information on the Net concerning Objective-C?
 22  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 to
    Smalltalk.

    Objective-C includes, when compared to C, a few more keywords and
    constructs, a short description of which follows.  For a complete example
    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), the
    layout of the instance variables (similar to the definition of a struct,
    but including encapsulation information (see Q6)) and declares the
    methods implemented by this class.  A class' interface usually resides
    in a file called `<classname>.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 `<classname>.m'.

    A `@category' is a named collection of method definitions which are
    added to an existing class.  With the NeXT runtime, a category can
    redefine existing methods.  However, with the GNU runtime, a category
    can not do so.

    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 message
    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 a
    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.

2   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++ an object's static type as
    perceived by the sender of a message determines which method will
    actually be invoked; this is static binding.  In Smalltalk the actual
    type of the object at run time determines the method, i.e. binding is
    dynamic.  As a result, in Smalltalk objects are not even statically
    typed; (in Objective-C static typing is optional).  The Simula 67
    school is safer, since static typing is mandatory and 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).  The truth lies
    somewhere in the middle, with contemporary Objective-C programming
    practices employing dynamic binding (mandatory) and static typing.

    Pragmatic differences between Objective-C and C++ include:

    C++ has operator overloading.  Some consider this to be `syntactic
    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.  The
    following is a list of the features `taken' from Smalltalk:

      * Objective-C is compiled---Smalltalk is only partially compiled.  The
    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 an
    object, the program would probably run at a speed comparable to
    Smalltalk and it would suffer from not having optimizations
    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 like
    `a:method:name:', as does Objective-C.  In Objective-C, the message
    sending construct is enclosed in square brackets, like this:
    `[anObject aMessage: arg]' whereas Smalltalk uses something like
    `anObject aMessage: arg'.

      * The basic class hierarchy, that is, having class `Object' in the very
    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, such
    functionality is implemented by `forward::'.

      * 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 definitions
    (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 a
        class' functionality in a way anticipated by the designer of
        that class, without the need for subclassing.  One can, of
        course, be the delegate of several objects of different
        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 quite
    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's
                class or a subclass thereof have access to
                the instance variables.
        @private    only methods of this class may access the
                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 programmer
    can only show his/her intention of making specific methods not
    public by not advertising them in the class' interface.  In
    addition, so-called private methods can be put in a category with a
    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 any
    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 multiple
    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 you
    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 simple
    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 <Archiving>
    @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 <Archiving> obj2 = obj1;

    // Error: obj1 does not conform to the TargetAction protocol.
    id <TargetAction> 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 name
    conflicts:

    @interface Foo: Object
    -(int) type;
    @end

    @protocol Bar
    -(const char *) type;
    @end

    -blah1: d
    {
      id t = [d someMethod];
      do_something_with ([t type]);
    }

    -blah2: d
    {
      id <Bar> 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 Environment

        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/tl.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 some
    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 (which is a modified gdb);
    Stepstone doesn't; for GNU, patches are available to turn gdb 4.16
    into an Objective-C aware debugger.

    NeXTSTEP (from version 3.0) and GCC (from version 2.4) support protocols
    and forward declarations of classes, Stepstone currently does not.

10  How do I debug Objective-C using a non-NeXT gdb.

    On August 20 1996, Michael Snyder of NeXT posted patches to GDB 4.16
    to make it Objective-C aware for GNU Objective-C code, at least tested
    on HP-UX, Solaris and MS Windows.  As he did not supply a net.address
    for these patches, I've made them available as
    ftp://ftp.es.ele.tue.nl/pub/objc/gdb-gnu-objc.diff.gz.uue, accompanied
    by ftp://ftp.es.ele.tue.nl/pub/objc/gdb-gnu-objc.README.

    Debugging Objective-C using a non-Objective-C aware gdb has been
    documented by Martin Cracauer <[e-mail]> on
    http://www.cons.org/cracauer/objc-hint-gdb.html.  (It comes down to
    understanding that you can very well look at Objective-C from the C
    perspective, a language very well understood by gdb.)

11  I get this `Floating exception'...

    Then you're running Linux and adding `-lieee' to the linker invocation
    could help.  Thomas March <[e-mail]> reported that on several
    occasions, on systems running Linux ELF, with libc.so.5.0.9 and
    libm.so.5.?.?, the problem was reproducable and adding `-lieee' did not
    solve the problem.  However, switching to a newer libc (libc.so.5.2.18
    and libm.so.5.0.5) both solved the problem and removed the need for
    `-lieee' (i.e. a back to normal situation).

    If the problem you're having does not fit either description given, ask.

12  Why am I lectured by gcc about `#import'?

    GNU CC issues the following multi-line warning about the how the use
    of `#import' is discouraged (output from GNU CC 2.7.0):

    foo.m:1: warning: using `#import' is not recommended
    The fact that a certain header file need not be processed more than once
    should be indicated in the header file, not where it is used.
    The best way to do this is with a conditional of this form:

      #ifndef _FOO_H_INCLUDED
      #define _FOO_H_INCLUDED
      ... <real contents of file> ...
      #endif /* Not _FOO_H_INCLUDED */

    Then users can use `#include' any number of times.
    GNU C automatically avoids processing the file more than once
    when it is equipped with such a conditional.

    In short, use `-Wno-import' as an argument to gcc to stop it from
    producing this.  Another possibility is to compile gcc after having
    changed the line reading `static int warn_import = 1' into `static
    int warn_import = 0' in `cccp.c' (line 467 in GNU CC 2.7.1); this way,
    `-Wno-import' is the default setting.

    Whether or not using `#import' is desirable (obviously) has to do with
    how to prevent multiple inclusions of the same file.  Most include
    files, when included multiple times, either do nothing new (possibly
    due to guards being used) or (without the guards) cause the emission
    of C code on which the compiler will choke (due to, for instance,
    repeated typedefs).  Thus, if everybody were to use `#import'
    everybody would be happy, since it does not seem to matter.  However,
    a notable exception to this rule is `assert.h', which changes the
    definition of the `assert' macro depending on the setting of the
    NDEBUG macro.

    There is one point to be made in favour of the warning: if the _user_
    of an include file uses `#include' instead of `#import', the guards
    will be necessary.  Thus, actually, the warning should be issued when
    a file is imported that appears not to be guarded.

    Apart from the more-or-less religious (and thus useless) debate
    whether `#import' or `#include'-with-guards is better, it has been
    observed that `#import' does not catch re-reading a linked and/or
    duplicated file, whereas the guards do.  However, this is, of course,
    a highly unlikely and probably undesirable situation for which neither
    was designed to catch.

    The reason for the existence of `#import' probably is historical: the
    first implementation of Objective-C (by Stepstone) was as a preprocessor
    to C, run after a modified cpp.  `#import' was the include-once
    directive to that cpp.  Since it is part of the Objective-C language, it
    has made it into GNU CC's cpp.

13  Did NeXT buy Stepstone?

    No they didn't!

    NeXT did acquire all rights previously owned by Stepstone to the
    Objective-C trademark and Objective-C language.  More information on
    `http://www.next.com/AboutNeXT/PressKit/PressReleases/1995/stepstone.040495.html'.

14  What written information concerning Objective-C is available?

    Books on Objective-C, or object oriented programming in general:

    Brad J. Cox, Andrew J. Novobilski: Object Oriented Programming: An
    Evolutionary Approach.  Addison-Wesley Publishing Company, Reading,
    Massachusetts, 1991.  ISBN: 0-201-54834-8 (Japanese: 4-8101-8046-8).

    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 (Japanese: 4-8101-8054-9).

    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 (Japanese: 4-8101-8048-4).

    abstract:       An intro to the topic of OOP, as well as a comparison
                    of C++, Objective-C, Smalltalk, and Object Pascal

    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 (Japanese: 4-7952-9636-7).  This is also
    available on the World Wide Web at
    http://www.next.com/Pubs/Documents/OPENSTEP/ObjectiveC/objctoc.htm.

    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.

    Articles

    `Why I need Objective-C', by Christopher Lozinski.
    Journal of Object-Oriented Programming (JOOP) September 1991.
    Contact [e-mail] 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 an
            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 [e-mail].

    Abstract:    This article describes how to develop Objective-C
            applications for both Microsoft Windows and
            NEXTSTEP.

    GNU Documentation

    The GNU project needs a free manual describing the Objective-C
    language features.  Because of its cause, GNU cannot include the
    non-free books in the GNU system, but the system needs to come with
    documentation.

    Anyone who can write good documentation, please think about giving
    it to the GNU project.  Contact [e-mail].

15  What kind of Objective-C support is provided by Stepstone?

    Compilers and runtime for: Apple Macintosh (running Mac Programmers
    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, OS/2), PS/2 (AIX), 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
    [phone] - (800) BUY-OBJEct voice / [phone] fax
    75 Glen Road
    Sandy Hook, CT 06482

16  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 the
    ClassWare Listing (part 2 of this FAQ).

    The sources to the NeXT-modified GNU products are available on the
    developer CD, and from
    ftp://ftp.next.com/pub/SoftwareDownloads/GNUSource/.

    Products are:

        NEXTSTEP 3.3, Mach/OpenStep 4.x, OpenStep/NT, Enterprise
        Objects Framework (EOF), Portable Distributed Objects (PDO),
        and WebObjects.

    NeXT Computer, Inc.
    900 Chesapeake Drive
    Redwood City, CA 94063
    tel: 800 848 NEXT
    fax: [phone]
    email: [e-mail]
    www: http://www.next.com/

17  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 2.7.2.1) includes an
    Objective-C compiler and runtime library.  The latter includes the
    `Object' and `NXConstantString' classes.  In future distributions the
    runtime library will be thread-safe.  Some people are working on GNU
    libraries, see part 2 of this FAQ (The ClassWare Listing) for details
    or visit http://www.gnustep.org/.

    If you haven't switched to a GNU CC as recent as 2.4 yet, here's one
    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
    59 Temple Place -- Suite 330
    Boston, MA   02111
    [phone]

    General questions about the GNU Project can be asked to
    [e-mail].

    For information on how to order GNU software on tape or cd-rom, and
    printed GNU manuals, check the file etc/ORDERS in the GNU Emacs
    distribution, ftp the file /pub/gnu/GNUinfo/ORDERS on prep, or e-mail
    a request to: [e-mail]

    By ordering your GNU software from the FSF, you help us continue to
    develop more free software.  Media revenues are our primary source of
    support.  Donations to FSF are deductible on US tax returns.

    The above software will soon be at these ftp sites as well.  Please
    try them before prep.ai.mit.edu as prep is very busy!

      thanx [e-mail]

        ASIA: ftp.cs.titech.ac.jp, tron.um.u-tokyo.ac.jp/pub/GNU/prep
     cair-archive.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/mirrors/uunet/systems/gnu,
     src.doc.ic.ac.uk/gnu, ftp.ieunet.ie:pub/gnu, ftp.eunet.ch,
     nic.sunsite.cnlab-switch.ch/mirror/gnu, ftp.win.tue.nl/pub/gnu,
     ftp.nl.net, ftp.informatik.rwth-aachen.de/pub/gnu,
     ftp.informatik.tu-muenchen.de, ftp.etsimo.uniovi.es/pub/gnu,
     ftp.funet.fi/pub/gnu, ftp.denet.dk, ftp.stacken.kth.se,
     isy.liu.se, ftp.luth.se/pub/unix/gnu,
     ftp.sunet.se/pub/gnu, archive.eu.net
        SOUTH AMERICA: ftp.inf.utfsm.cl/pub/gnu, 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, uiarchive.cso.uiuc.edu/pub/gnu,
     ftp.cs.columbia.edu/archives/gnu/prep,
     archive.cis.ohio-state.edu/pub/gnu, gatekeeper.dec.com/pub/GNU,
     ftp.uu.net/systems/gnu

    [GNU FTP mirror site list dd Tue Jan 13 1997.]

18  Is Objective-C supported on <my favourite platform>?

    Below is a list of compilers supporting Objective-C, and which are not
    NeXT's, Stepstone's or plain GCC.  [This section is being edited.]

    Various platforms

        Portable Object Compiler

        The Portable Object Compiler runs on various UNIX platforms,
        including AIX, OSF/1, Linux, NextStep, IRIX, HP-UX, SunOS and
        Solaris.  It is currently being ported to BeOS and WindowsNT.

        The Portable Object Compiler is freely obtainable (comes with
        source) from the Computer Algebra Objects website, currently
        at, http://www.can.nl/~stes.

        Included is a collection library, ObjectPak which compiles on,
        and works with, Stepstone Objective C, GNU Objective C and
        NeXT Objective C.  This library also comes with source code.

        [The Portable Object Compiler does not provide protocols.]

    DOS, Windows, OS/2

    BPG

        BPG provides the Borland Extensions to Objective-C which
        allows the Objective-C translator to be used with the Borland
        Compiler, and makes 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 messages 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 94560
        Tel: [phone]
        fax: [phone]
        email: [e-mail]

    DJGPP

        DJGPP includes Objective-C support [though I do not know to
        which extent].

        From the DJGGP homepage at http://www.delorie.com:

        DJGPP is a complete 32-bit C/C++ development system for
        Intel 80386 (and higher) PCs running DOS. It includes
        ports of many GNU development utilities. The development
        tools require a 80386 or newer computer to run, as do the
        programs they produce. In most cases, the programs it
        produces can be sold commercially without license or
        royalties.

    GCC/EMX

        The EMX port of GCC implements Objective-C, and with RSX (or
        RSXNT) it runs on DOS/DPMI boxes (or NT) too.

        EMX is available for anonymous ftp on at following locations:

        ftp://ftp.uni-stuttgart.de/pub/systems/os2/emx-0.9c
        ftp://ftp-os2.cdrom.com/pub/os2/lang/emx09c
        ftp://ftp-os2.nmsu.edu/os2/unix/emx09c
        ftp://ftp.leo.org/pub/comp/os/os2/devtools/emx+gcc
        ftp://src.doc.ic.ac.uk/packages/os2/unix/emx09c

        RSX is available from
        ftp://ftp.uni-bielefeld.de/pub/systems/msdos/misc/
        Without RSX EMX is limited to DOS/VCPI and OS/2 >=2.0)

        [Thanks to <[e-mail]> for this information.]

    GCC for Win32

        Hyungjip Kim <[e-mail]> provides GCC 2.7.2 binaries
        for Win32.  This GCC is modified to generate CodeView
        compatible debug information, to enable the use of existing
        Windows debuggers.  Visit http://www.namo.co.kr/~hjkim/objc/
        for more information, and the binaries.

    GNU-Win32

        The GNU-Win32 project aims at providing the GNU tools
        (including GCC) for Windows NT/95.  [I do not know to which
        extent Objective-C is supported.]  Below is a description of
        the project, taken from http://www.cygnus.com/misc/gnu-win32:

        The GNU-Win32 tools are ports of the popular GNU
        development tools to Windows NT/95 for the x86 and powerpc
        processors. Applications built with these tools have
        access to the Microsoft Win32 API as well as the Cygwin32
        API which provides additional UNIX-like functionality
        including UNIX sockets, process control with a working
        fork and select, etc...

        With these tools installed, it is now possible to:

        write Win32 console or GUI applications that make use of
        the standard Microsoft Win32 API and/or the Cygwin32 API.

        easily configure and build many GNU tools from source
        (including rebuilding the gnu-win32 development tools
        themselves under x86 NT).

        port many other significant UNIX programs to Windows NT/95
        without making significant changes to the source code.

        have a fairly full UNIX-like environment to work in, with
        access to many of the common Unix utilities (from both the
        bash shell and command.com).

        The GNU-Win32 project is run by Cygnus; for more information
        see http://www.cygnus.com.

    Macintosh

    With the recent acquirement of NeXT by Apple, support of
    Objective-C on the Macintosh will boom.  Undoubtebly Apple will
    provide Objective-C support, and Metrowerks have announced support
    for Objective-C in their CodeWarrior.

19  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, [e-mail], discussing this
    very topic.  To subscribe to this list, send a mail with your request to
    `[e-mail].'

    Furthermore, the various kits that are being developed each come with
    their own mailing list.  See part 2 of this FAQ for more information.

20  Are there any FTP sites with Objective C code?  Where?

    ftp://next-ftp.peak.org/pub/next/    (NEXTSTEP)
    ftp://ftp.informatik.uni-muenchen.de
    ftp://ftp.gnustep.org/pub/        (GNUStep)
    ftp://ftp.stack.urc.tue.nl/pub/next/    (NEXTSTEP)
    ftp://ccrma-ftp.stanford.edu/pub/NeXT/    (MusicKit a.o.)
    ftp://ftp.informatik.uni-freiburg.de
    ftp://ftp.cs.unl.edu/pub/ObjC        (some sw and docs)

    See also part 2 of this FAQ.

21  If there any information on the Net concerning Objective-C?

    Basic and related Objective-C (and/or NeXTSTEP) information is available
    at the following places:

    NeXT at http://www.next.com/ with the NeXT Objective-C book at
    http://www.next.com/Pubs/Documents/OPENSTEP/ObjectiveC/objctoc.htm,

    Steve deKorte's Objective-C page at
    http://www.batech.com/~dekorte/Objective-C/objc.html,

    Brad Cox's Objective-C page at
    http://www.virtualschool.edu/mon/Cox/ObjectiveC.html,

    the GNUStep project at http://www.gnustep.org/, with a mirror at
    http://www.nmr.embl-heidelberg.de/GNUstep

    the libobjects FAQ at
    ftp://ftp.cs.rochester.edu/pub/u/mccallum/libobjects/Gnustep-FAQ.html,

    the NEXTSTEP/OpenStep Information Service at http://www.stepwise.com/,

    the eduStep initiative at http://www.nmr.embl-heidelberg.de/eduStep/,

    Nelson Minar's Objective-C page at
    http://www.santafe.edu/~nelson/objective-c.html,

    Tiggr's Objective-C page at http://www.es.ele.tue.nl/tiggr/objc/,

    Kennet Lerman's page at http://w3.nai.net/~lerman/,

    Norihiro Itoh's page at http://www.etl.go.jp/etl/bunsan/~nito/,

    and of course the HTML versions of this FAQ and associated information
    at the addresses listed below.

22 For more information...

    Visit one of the places mentioned in #21, or see part 2 of this FAQ,
    Objective-C/classes a.k.a. the ClassWare Listing, for an [incomplete!]
    overview of available Objective-C classes and libraries.  See part 3 of
    this FAQ, Objective-C/sample a.k.a. the Simple Sample Program, for an
    example Objective-C program.

A Japanese language version of this FAQ is maintained by Norihiro Itoh
<[e-mail]>.  It is posted to fj.archives.answers regularly.  A
hypertext version is maintained by Toru Sato <[e-mail]>
and is available at
http://www.cnds.canon.co.jp/Japanese_EUC/Contribution/FAQ_Objective-C/objc_faq_J.html.

A World Wide Web hypertext version of this FAQ is maintained by Brian Harvey
<[e-mail]>.  It is http://csld.ucr.edu/NeXTSTEP/objc_faq.html.
Another WWW version of this FAQ is maintained by Steve Dekorte
<[e-mail]> at http://www.batech.com/~dekorte/Objective-C/objc.html.

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 input
from a lot of people, including: Per Abrahamsen, Paul Burchard, Brad Cox,
Christopher Lozinski, Mike Mahoney, Jon F. Rosen, Paul Sanchez, Lee Sailer,
Paul Sanchez, Bill Shirley, Subrata Sircar, Ted Slupesky, Richard Stallman,
and Kersten Krab Thorup,

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 `[e-mail]'.

    The information in this file comes AS IS, WITHOUT ANY WARRANTY.  You may
    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.