Useful macros

When working with the Boehm's garbage collector, the messages used by the reference counting mechanism are obsolete and they simply introduce an unnecessary overhead. That's why instead of sending the retain, release and autorelease messages you'd better use the macros with the similar names, RETAIN, RELEASE and AUTORELEASE. When the code is compiled with support for Boehm's garbage collector the correspondent messages are not sent at all.

In addition to the above macros, another macro should be used to make the code cleaner. The ASSIGN macro can be used whenever an object value is assigned to an object variable and the old value of the variable needs to be release and the new value retained. The definition of this macro is:

#define ASSIGN(object, value) \
  ({if (value) [value retain]; \
    if (object) [object release]; \
    object = value;})

When Boehm's garbage collector is used the definition of the macro is simply:

#define ASSIGN(object, value) \
  object = value

Another macro can be used whenever the code requires the creation of an autorelease pool. This pool is not needed when the code works in the presence of Boehm's garbage collector. The macro is CREATE_AUTORELEASE_POOL and should be used as a variable definition and must placed the last in the variables definition list. Use the RELEASE macro to release the pool.

The preprocessor define LIB_FOUNDATION_BOEHM_GC can be used to find out if the program is compiled with support for Boehm's garbage collector (See section Preprocessor defines for other preprocessor defines). If you need to find out at runtime if the program was compiled with support for Boehm's collector you can access the read-only variable _usesBoehmGC.

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