Inoussa OUEDRAOGO wrote:
2009/6/29 Tom Verhoeff <t.verho...@tue.nl>:
While tracing a nasty bug (?), I discovered the hard way that when
an Assert is done in a constructor, and it fails, then the destructor
(Destroy) is automatically called.
Indeed, when an exception is raised in the constructor, be it an
"assert" exception or not, the destructor is called to allow the
developer to clean up the "in-construction" instance's members he has
already initialized.
I just cam across this thread. While I am not opposing the behaviour as
it's stand (it could be useful anyway), it raises another question.
Does that mean that an implicit exception-frame (or whatever this is
called) is inserted *each* time you create/instantiate an object?
Now I understand, object instantiation comes at a cost anyway (memory
allocation), this does add to the cost of instantiation. And the only
error/exception, which really *all* classes can encounter in a
constructor, is out of memory for the object itself => In which case
create is never called (because NewInstance fails), and Destroy should
not be called (as there is no instance that could be passed to destroy).
So There could be calls to create where a developer does not want (and
not need) any exception stack frame.
I also wonder why this special kind of "garbage collector"? Pascal has
automatic behaviour to handle/free resources for:
- strings
- open array
- apparently classes/objects, but only inside the constructor ?
The last one does of course not apply to objects hold by the failed
object, but I assume that, if Destroy is called, the instance is also freed?
So why are objects handled special in the constructor? If they raise an
exception anywhere else in there live, then you need to care yourself
about catching it, and freeing them?
Anyway, as I said it's not necessarily bad behaviour. but given that
exception handling may add to runtime cost, is there a way to switch
this off?
Like
{$AutoDestroty off}
try
foo := TFoo.create;
except
if foo <> nil then foo.free;
end;
Martin
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