Next: Synchronization, Previous: compatibility_alias, Up: Objective-C [Contents][Index]
GNU Objective-C provides exception support built into the language, as in the following example:
@try {
@throw expr;
}
@catch (AnObjCClass *exc) {
@throw expr;
@throw;
}
@catch (AnotherClass *exc) {
}
@catch (id allOthers) {
}
@finally {
@throw expr;
}
The @throw statement may appear anywhere in an Objective-C or Objective-C++ program; when used inside of a @catch block, the @throw may appear without an argument (as shown above), in which case the object caught by the @catch will be rethrown.
Note that only (pointers to) Objective-C objects may be thrown and caught using this scheme. When an object is thrown, it will be caught by the nearest @catch clause capable of handling objects of that type, analogously to how catch blocks work in C++ and Java. A @catch(id ) clause (as shown above) may also be provided to catch any and all Objective-C exceptions not caught by previous @catch clauses (if any).
The @finally clause, if present, will be executed upon exit from the immediately preceding @try @catch section. This will happen regardless of whether any exceptions are thrown, caught or rethrown inside the @try @catch section, analogously to the behavior of the finally clause in Java.
There are several caveats to using the new exception mechanism:
NS_HANDLER-style idioms provided by the NSException class, the new exceptions can only be used on Mac OS X 10.3 (Panther) and later systems, due to additional functionality needed in the NeXT Objective-C runtime.@throw an exception from Objective-C and catch it in C++, or vice versa (i.e., throw @catch).Next: Synchronization, Previous: compatibility_alias, Up: Objective-C [Contents][Index]