Objective-C Compiler and Runtime FAQ - Revision history

Thebeing: ObjC2 FAQ moved to Objective-C Compiler and Runtime FAQ

2015-11-29T14:05:08Z

ObjC2 FAQ moved to Objective-C Compiler and Runtime FAQ

Thebeing at 14:03, 29 November 2015

2015-11-29T14:03:45Z

Mitchell-riley: fixed inaccuracies

2015-06-04T19:59:57Z

fixed inaccuracies

Mitchell-riley: Reverting to normalized titles

2015-06-04T19:54:58Z

Reverting to normalized titles

Mitchell-riley at 23:52, 24 February 2015

2015-02-24T23:52:32Z

Mitchell-riley at 01:02, 19 February 2015

2015-02-19T01:02:22Z

Fedor: /* Where can I get it */

2013-12-22T17:18:13Z

Where can I get it

Fedor: Fix version

2013-12-22T03:33:56Z

Fix version

Fedor: Add download location

2013-12-22T02:44:55Z

Add download location

Rfm: /* Can I use Apple's Runtime APIs? */

2010-06-11T09:46:34Z

Can I use Apple's Runtime APIs?

@@ Line 8: / Line 8: @@
 ----------------------------
-If you have used Objective-C on Mac OS X, then you will have used one or both of Apple's two Objective-C runtimes.  The Apple legacy runtime is based on the version implemented by NeXT back in the '80s, although it has seen some improvements since that time and is often referred to as the NeXT runtime.  Apple's modern runtime is a complete rewrite, introduced with OS X 10.5.  The modern runtime is required for Objective-C 2 and is the default on 64-bit platforms.
+If you have used Objective-C on Mac OS X, then you will have used one or both of Apple's two Objective-C runtimes.  The Apple legacy runtime is based on the version implemented by NeXT back in the '80s, although it has seen some improvements since that time and is often referred to as the NeXT runtime.  Apple's modern runtime is a complete rewrite, introduced with OS X 10.5.  The modern runtime is required for modern Objective-C features such as properties, fast enumeration, or ARC (automated reference counting) and is the default on 64-bit platforms. The first set of new features (properties, dot-notation, fast enumeration, garbage collection) was originally marketed by Apple as ‘Objective-C 2’, even though the last version shipped by NeXT was actually Objective-C 4.
-The implementation of Objective-C produced by NeXT was based on GCC and as such NeXT was required to release the relevant compiler changes.  The NeXT Objective-C runtime was not open sourced (it was later, after Apple bought NeXT, but the code is not particularly portable and so is not used on platforms other than Darwin) and so the GNU project created a new one, generally referred to as the GNU runtime.
+The implementation of Objective-C produced by NeXT was based on GCC and as such NeXT was required to release the relevant compiler changes. The NeXT Objective-C runtime was not open sourced (it was later, after Apple bought NeXT, but the code is not particularly portable and so is not used on platforms other than Darwin) and so the GNU project created a new one, generally referred to as the GNU runtime.
 === Which Runtime Should I use? ===
 ---------------------------
-If you are using a recent version of GCC to compile your code then you should have a copy of the Objective-C runtime library that came with your compiler.
+If you are using a very old version of GCC then you may need to use a newer version of GNU runtime.  If you experience problems with the version of runtime that came with your compiler and you don't need support for the modern language features, then you should install libobjc from GNUstep subversion (libs/libobjc/trunk).  This is a copy of version 1.6 of the GCC runtime which is modified to build outside the GCC tree.
-If you are using a very old version of GCC then you may need to use a newer version of GNU runtime.  If you experience problems with the version of runtime that came with your compiler, then you should install libobjc from GNUstep subversion (libs/libobjc/trunk).  This is a copy of version 1.6 of the GCC runtime which is modified to build outside the GCC tree.
+If you want to make use of fast enumeration or declared properties, you can use the GCC runtime and GCC 4.6 or later.
-For more advanced features, currently only supported if you compile with Clang, you will need the GNUstep runtime.  This is not currently considered production ready.  It should work as a drop-in replacement for the GCC runtime, but some of the advanced features are not well-tested.
+More advanced features, such as automatic reference counting (ARC), non-fragile instance variables, or blocks require that you use the GNUstep runtime and clang as the compiler.
 === What is or was the Étoilé Runtime? ===
@@ Line 77: / Line 78: @@
 ------------------------------
-GNUstep has supported garbage collection via the [http://www.hboehm.info/gc/ Boehm GC] for some years.  Efforts are underway to bring this to closer compatibility with Apple's new implementation.
+GNUstep has supported garbage collection via the [http://www.hboehm.info/gc/ Boehm GC] for some years. The GNUstep runtime also supports a GC mode similar to the one by introduced by Apple. Since Apple has deprecated the GC mode in Mac OS X 10.8 in favour of ARC, it should no longer be used.
 === Where can I get it ===
 ------------------------------
-You may obtain the code for the modern Objective-C runtime from subversion at the following
+You may obtain the code for the modern Objective-C runtime from github:
-[http://download.gna.org/gnustep/libobjc2-1.7.txz txz]
+https://github.com/gnustep/libobjc2/releases

@@ Line 41: / Line 41: @@
 * Clang
-The latter two use the Low-Level Virtual Machine ([http://llvm.org/ LLVM]) for code generation.  This is a BSD-licensed compiler infrastructure used by several other projects.  LLVM-GCC is a hybrid, using Apple's version of GCC for parsing and LLVM for optimisation and native code generation.  Clang is a new front end for LLVM.
+The latter two use the [http://llvm.org/ Low Level Virtual Machine] for code generation.  This is a BSD-licensed compiler infrastructure used by several other projects.  LLVM-GCC is a hybrid, using Apple's version of GCC for parsing and LLVM for optimisation and native code generation.  Clang is a new front end for LLVM.
 Currently, LLVM-GCC is based on Apple's GCC and so does not support the GNU runtime.  There is an effort underway to rewrite LLVM-GCC as a plugin for GCC 4.5, at which point it should support as much Objective-C as GCC currently does.
@@ Line 54: / Line 54: @@
 If you compile with Clang then you have access to declared properties, fast enumeration, and blocks.  Note that both of these require some support from the runtime.  This must be provided either by the GNUstep runtime or by the ObjectiveC2 framework, which you can acquire from Étoilé subversion.  For blocks to work, you must also compile with -fblocks.
-If you link with the -fobjc-nonfragile-abi flag then you will use the new ABI.  This is only supported with the GNUstep runtime.  This adds:
+If you compile with the -fobjc-nonfragile-abi flag then you will use the new ABI.  This is only supported with the GNUstep runtime.  This adds:
 * Property introspection

@@ Line 5: / Line 5: @@
 * '''Runtime Library''' - responsible for things like message sending and introspection
-=== How Many Runtimes Are There? ===
+=== How Many Runtimes Are there? ===
 ----------------------------
@@ Line 14: / Line 14: @@
 In 2009, a fork of this was committed to GNUstep subversion repository as libobjc2.  This contains a lot of new features and removes a lot of legacy code, but is not yet considered production ready.  Unlike the original GNU runtime (which will be referred to as the GCC runtime, for differentiation), this can be built outside of the GCC tree and distributed independently.  The GNUstep runtime supports two ABIs.  One is compatible with the GCC runtime, the other is new and is designed to support Objective-C 2.
-=== Which Runtime Should I Use? ===
+=== Which Runtime Should I use? ===
 ---------------------------
@@ Line 23: / Line 23: @@
 For more advanced features, currently only supported if you compile with Clang, you will need the GNUstep runtime.  This is not currently considered production ready.  It should work as a drop-in replacement for the GCC runtime, but some of the advanced features are not well-tested.
-=== What is or Was the Étoilé Runtime? ===
+=== What is or was the Étoilé Runtime? ===
 ----------------------------------
@@ Line 63: / Line 63: @@
 Unlike Apple's non-fragile ABI, it is possible to mix code compiled for our fragile and non-fragile ABIs with some caveats.  Message sending from code compiled with the fragile ABI will not be able to take advantage of forwarding proxies.  If you subclass a non-fragile ABI class with a class compiled with the fragile ABI then you will not receive any benefits; the class compiled with the fragile ABI must be able to see all of the instance variables in the superclass at compile time or things will break.  Some benefits will be obtained the other way around, however.  A class compiled for the fragile ABI will always be able to access its own instance variables safely when the superclass changes, even if the superclass layout changes.  It will, however, only be able to safely access instance variables declared in superclasses safely if the superclass is also compiled with the non-fragile ABI or if the superclass instance variable layout does not change.
-=== Can I Use Apple's Runtime APIs? ===
+=== Can I use Apple's Runtime APIs? ===
 -------------------------------
@@ Line 79: / Line 79: @@
 GNUstep has supported garbage collection via the [http://www.hboehm.info/gc/ Boehm GC] for some years.  Efforts are underway to bring this to closer compatibility with Apple's new implementation.
-=== Where Can I Get It ===
+=== Where can I get it ===
 ------------------------------
@@ Line 89: / Line 89: @@
 Alternatively, a tarball is available from:
-* [http://download.gna.org/gnustep/libobjc2-1.7.txz txz]
+[http://download.gna.org/gnustep/libobjc2-1.7.txz txz]
-* [http://download.gna.org/gnustep/libobjc2-1.7.tar.bz2 bz2]
+[http://download.gna.org/gnustep/libobjc2-1.7.tar.bz2 bz2]
-* [http://download.gna.org/gnustep/libobjc2-1.7.tgz tgz]
+[http://download.gna.org/gnustep/libobjc2-1.7.tgz tgz]

@@ Line 5: / Line 5: @@
 * '''Runtime Library''' - responsible for things like message sending and introspection
-=== How Many Runtimes Are there? ===
+=== How Many Runtimes Are There? ===
 ----------------------------
@@ Line 14: / Line 14: @@
 In 2009, a fork of this was committed to GNUstep subversion repository as libobjc2.  This contains a lot of new features and removes a lot of legacy code, but is not yet considered production ready.  Unlike the original GNU runtime (which will be referred to as the GCC runtime, for differentiation), this can be built outside of the GCC tree and distributed independently.  The GNUstep runtime supports two ABIs.  One is compatible with the GCC runtime, the other is new and is designed to support Objective-C 2.
-=== Which Runtime Should I use? ===
+=== Which Runtime Should I Use? ===
 ---------------------------
@@ Line 23: / Line 23: @@
 For more advanced features, currently only supported if you compile with Clang, you will need the GNUstep runtime.  This is not currently considered production ready.  It should work as a drop-in replacement for the GCC runtime, but some of the advanced features are not well-tested.
-=== What is or was the Étoilé Runtime? ===
+=== What is or Was the Étoilé Runtime? ===
 ----------------------------------
@@ Line 63: / Line 63: @@
 Unlike Apple's non-fragile ABI, it is possible to mix code compiled for our fragile and non-fragile ABIs with some caveats.  Message sending from code compiled with the fragile ABI will not be able to take advantage of forwarding proxies.  If you subclass a non-fragile ABI class with a class compiled with the fragile ABI then you will not receive any benefits; the class compiled with the fragile ABI must be able to see all of the instance variables in the superclass at compile time or things will break.  Some benefits will be obtained the other way around, however.  A class compiled for the fragile ABI will always be able to access its own instance variables safely when the superclass changes, even if the superclass layout changes.  It will, however, only be able to safely access instance variables declared in superclasses safely if the superclass is also compiled with the non-fragile ABI or if the superclass instance variable layout does not change.
-=== Can I use Apple's Runtime APIs? ===
+=== Can I Use Apple's Runtime APIs? ===
 -------------------------------
@@ Line 79: / Line 79: @@
 GNUstep has supported garbage collection via the [http://www.hboehm.info/gc/ Boehm GC] for some years.  Efforts are underway to bring this to closer compatibility with Apple's new implementation.
-=== Where can I get it ===
+=== Where Can I Get It ===
 ------------------------------
@@ Line 89: / Line 89: @@
 Alternatively, a tarball is available from:
-[http://download.gna.org/gnustep/libobjc2-1.7.txz txz]
+* [http://download.gna.org/gnustep/libobjc2-1.7.txz txz]
-[http://download.gna.org/gnustep/libobjc2-1.7.tar.bz2 bz2]
+* [http://download.gna.org/gnustep/libobjc2-1.7.tar.bz2 bz2]
-[http://download.gna.org/gnustep/libobjc2-1.7.tgz tgz]
+* [http://download.gna.org/gnustep/libobjc2-1.7.tgz tgz]

@@ Line 1: / Line 1: @@
 == Objective-C Compiler and Runtime FAQ ==
+An Objective-C implementation comes in two components:
-An Objective-C implementation comes in two components; a compiler and a runtime library.  The compiler is responsible for parsing the source code and produces a binary that contains calls to the functions in the runtime library.  This library is responsible for things like message sending and introspection.
+* '''Compiler''' - responsible for parsing the source code and produces a binary that contains calls to the functions in the runtime library
 === How Many Runtimes Are there? ===
@@ Line 40: / Line 41: @@
 * Clang
-The latter two use the Low-Level Virtual Machine (LLVM) for code generation.  This is a BSD-licensed compiler infrastructure used by several other projects.  LLVM-GCC is a hybrid, using Apple's version of GCC for parsing and LLVM for optimisation and native code generation.  Clang is a new front end for LLVM.
+The latter two use the Low-Level Virtual Machine ([http://llvm.org/ LLVM]) for code generation.  This is a BSD-licensed compiler infrastructure used by several other projects.  LLVM-GCC is a hybrid, using Apple's version of GCC for parsing and LLVM for optimisation and native code generation.  Clang is a new front end for LLVM.
-Currently, LLVM-GCC is based on Apple's GCC and so does not support the GNU runtime.  There is an effort underway to rewrite LLVM-GCC as a plug in for GCC 4.5, at which point it should support as much Objective-C as GCC currently does.
+Currently, LLVM-GCC is based on Apple's GCC and so does not support the GNU runtime.  There is an effort underway to rewrite LLVM-GCC as a plugin for GCC 4.5, at which point it should support as much Objective-C as GCC currently does.
-Unlike GCC, Clang features a clean abstraction layer between the runtime-specific and runtime-agnostic parts of the compiler.  This means that adding support for new features on the GNU runtime is simply a matter of implementing the relevant methods in the CGObjCGNU class.  This means that Clang is able to support almost everything on the GNUstep runtime that it does on either of the Apple runtimes.  Note, however, that Clang only recently reached version 1.0 status.  Current subversion builds are more stable, but things like generating debugging info are still somewhat unreliable.
+Unlike GCC, Clang features a clean abstraction layer between the runtime-specific and runtime-agnostic parts of the compiler.  This means that adding support for new features on the GNU runtime is simply a matter of implementing the relevant methods in the CGObjCGNU class.  This means that Clang is able to support almost everything on the GNUstep runtime that it does on either of the Apple runtimes.
 === Which Bits of Objective-C 2 Work? ===
@@ Line 53: / Line 54: @@
 If you compile with Clang then you have access to declared properties, fast enumeration, and blocks.  Note that both of these require some support from the runtime.  This must be provided either by the GNUstep runtime or by the ObjectiveC2 framework, which you can acquire from Étoilé subversion.  For blocks to work, you must also compile with -fblocks.
-If you compile with the -fobjc-nonfragile-abi flag then you will use the new ABI.  This is only supported with the GNUstep runtime.  This adds:
+If you link with the -fobjc-nonfragile-abi flag then you will use the new ABI.  This is only supported with the GNUstep runtime.  This adds:
 * Property introspection
@@ Line 76: / Line 77: @@
 ------------------------------
-GNUstep has supported garbage collection via the Boehm GC for some years.  Efforts are underway to bring this to closer compatibility with Apple's new implementation.
+GNUstep has supported garbage collection via the [http://www.hboehm.info/gc/ Boehm GC] for some years.  Efforts are underway to bring this to closer compatibility with Apple's new implementation.
 === Where can I get it ===

← Older revision	Revision as of 14:05, 29 November 2015
(No difference)

@@ Line 81: / Line 81: @@
 ------------------------------
-You may obtain the code for this release from subversion at the following
+You may obtain the code for the modern Objective-C runtime from subversion at the following
 subversion branch:

@@ Line 84: / Line 84: @@
 subversion branch:
-svn://svn.gna.org/svn/gnustep/libs/libobjc2/releases/1.8
+svn://svn.gna.org/svn/gnustep/libs/libobjc2/releases/1.7
 Alternatively, a tarball is available from:
-[http://download.gna.org/gnustep/libobjc2-1.8.txz txz]
+[http://download.gna.org/gnustep/libobjc2-1.7.txz txz]
-[http://download.gna.org/gnustep/libobjc2-1.8.tar.bz2 bz2]
+[http://download.gna.org/gnustep/libobjc2-1.7.tar.bz2 bz2]
-[http://download.gna.org/gnustep/libobjc2-1.8.tgz tgz]
+[http://download.gna.org/gnustep/libobjc2-1.7.tgz tgz]

← Older revision		Revision as of 02:44, 22 December 2013
Line 77:		Line 77:

	GNUstep has supported garbage collection via the Boehm GC for some years. Efforts are underway to bring this to closer compatibility with Apple's new implementation.		GNUstep has supported garbage collection via the Boehm GC for some years. Efforts are underway to bring this to closer compatibility with Apple's new implementation.
		+
		+	=== Where can I get it ===
		+	------------------------------
		+
		+	You may obtain the code for this release from subversion at the following
		+	subversion branch:
		+
		+	svn://svn.gna.org/svn/gnustep/libs/libobjc2/releases/1.8
		+
		+	Alternatively, a tarball is available from:
		+
		+	[http://download.gna.org/gnustep/libobjc2-1.8.txz txz]
		+	[http://download.gna.org/gnustep/libobjc2-1.8.tar.bz2 bz2]
		+	[http://download.gna.org/gnustep/libobjc2-1.8.tgz tgz]

@@ Line 64: / Line 64: @@
 === Can I use Apple's Runtime APIs? ===
 -------------------------------
 With OS X 10.5, Apple introduced a new set of APIs for interacting with the runtime.  These hid the implementation details - previously all public - behind a set of public functions, implemented on both the modern and legacy runtimes.
 These functions are supported by the GNUstep runtime and can also be used with the GCC runtime if you link against Étoilé's ObjectiveC2 framework.
 === What About Garbage Collection? ===