Comparison with False - something I don't understand

[Tim Harig]

On 2010-12-02, MRAB <python at mrabarnett.plus.com> wrote:
> On 02/12/2010 19:15, Tim Harig wrote:
>> On 2010-12-02, Paul Rubin<no.email at nospam.invalid>  wrote:
>>> Tim Harig<usernet at ilthio.net>  writes:
>>>>> longjmp.  Alternatively you can have an auxiliary stack of cleanup
>>>>> records that the longjmp handler walks through.  Of course if you do
>>>>
>>>> Only if you already have pointers to *all* of the data structures at
>>>> the point where you put your setjmp().
>>>
>>> The setjmp point only has to know where the aux stack is and its depth
>>> when the longjmp happens.  The cleanup records contain any necessary
>>> pointers to data structures that need freeing.  That is basically how
>>> try/finally would do it too.  This is pretty standard stuff.
>>
>> I am not talking about what setjmp() has to do, I am talking about what
>> *you* have to do after setjmp() returns.  If you have allocated memory in
>> intermediate functions and you don't have a reference to them outside of
>> the functions that longjmp() bypasses from returning properly (and thus
>> either not clearning data structures or returning a reference to those data
>> structures as it normally would) then you have potential memory leaks,
>> dangling pointers, etc.
>>
>> I am not saying that this cannot be done.  What I am saying is that it
>> is inherently error prone.
>
> Automatic garbage collection is nice to have when using exceptions
> precisely because it's automatic, so unwinding the stack is much safer.

Indeed.