Daniël Mantione wrote:
Op Sun, 5 Jun 2005, schreef Jamie McCracken:
yes but isn't it fair to say that such developers that require such
structures would be knowledgable enough to make it safe by using weak refs?
What is a weak ref?
Allows you to make a reference without increasing or affecting the ref
count of an object.
My point is that the everyday structures that most developers (and in
particular the more naive and less knowledgable ones) will use are not
vulnerable to cycles and its only the more obscure and specialised use
cases that will need to use weak refs. In those cases like building a
compiler is it reasonable to assume that they will be smart enough to
handle cycles with weak refs?
I don't know, anyway, structures like trees, graphs, stacks, ringbuffers,
linked lists etc. etc. are the basis of programming. A language that makes
using them hard or impossible becomes a toy language.
But it doesn't. The only time they are a problem is when the stuff you
are storing in the tree or list is an *object* and that *object* points
back to either the container or the list that stores it (which is very
rarely done). The most likely case for that is if you added a self
reference -
EG
mylist : Tlist;
mylist := TList.create;
mylist.add (mylist);
// now you have a self referencing cycle
The above could still be implemented safely in the add method of Tlist
by testing for a cycle and using a weak ref to add mylist to mylist. BUt
of course why would you ever want to add a self referencing cycle to a
TList?
Hmmm... Is a double linked list a cycle? I think yes.
I dont think so. The list nodes are usally a record/struct not an
*object* and whilst they do form a chain, the items pointed to in the
list dont point back to that list so no it is not a cycle.
Cycles are rare by the nature in objects however they are more common in
GUIs where widgets and components link together.
jamie.
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