I'm not clear about the semantics of the Objective-C exception-
handling constructs, even after going through the Apple Objective-C
documentation and the developer-doc conceptual "Exception Handling".
The definitions are very terse or missing and the examples are
incomplete. The problem with learning by example is that one has to
make hypotheses about general cases which is dangerous.
In particular, the examples show a series of @catch blocks arranged in
most-specific to least-specific order. Since the different blocks in
the example
have different parameter specifications for the different blocks this
seems to imply that there is some sort of filtering of which block to
invoke on an exception. It seems more likely to me that each
successive block must inspect the exception and if it does not apply,
ignore it, allowing the next @catch block to inspect and handle it.
However, the examples do not show this, and nothing is written to
indicate how to let the next block be invoked to inspect and handle or
ignore it. Again, I presume that this is accomplished by doing nothing
and falling off the end of the block. I don't like this as an
assumption, since this is an exception (no pun intended) to the normal
semantics - i.e., falling off the end of a procedure or method is
equivalent to an implicit "return". I'm not arguing against the syntax/
semantics here - I would just like to be sure about the semantics.
Does falling off the end of a
@catch block invoke the next @catch block ( or the @finally if there
are no more @catch blocks)?
The section on "Exception Handling With Macros" indicates the
alternatives for leaving the exception domain, but no such table
exists in the "Handling Exceptions Using Compiler Directives" It does
indicate that "return" or "goto" may be used, but not "setjmp or
longjmp". The semantics of "goto" seem problematic. I would assume
that one could "goto" a label in the @try block, but a "goto" to a
label in another "catch" block could be disastrous. My C manuals say
that it is illegal to "goto" out of the current function.
t appears (another assumption) that a "return" will exit the current
method.
Can anyone clear me up on this?
Regards,
Dale Miller
[EMAIL PROTECTED]
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