Gtk--: G_List quirks

[Some Guy <guy mikepery pr mcs net>]

(Tero, this is for you, I just posted here so everyone could have a look)

I was looking at the new G_List addon for gtk--, when I came across (I
think) a potential problem.  The G_List class is defined (partly) as
follows:

class G_List
{ 
  GList *list;
...
  G_List* next() { if(list->next) list = list->next; return this; }
  G_List* prev() { if(list->prev) list = list->prev; return this; }
...
}

The problem arises when you are using the G_List::next() and prev()
functions, thinking they will return a pointer to the next/prev node in
the list.  However, they don't only do that.  They first modify the glib
object, then do return this;.  This would work fine for someone doing the
following:
   for (list = container->children();
	list->glist() != NULL;
	list = list->next()) ...
Then it works as expected.  But what if someone only wanted a temporary
peek at the next/prev node?  For example:
   g_print("prev: %s\n", list->prev()->data());
   g_print("this: %s\n", list->data());
   g_print("next: %s\n", list->next()->data());
The first statement has the effect of doing
   g_print("prev: %s\n", (list = list->prev())->data);
as well as the last statement, which is surely not what you want in this
situation.  I'm not sure how often it will come up, but it probably will
show up some time.

I think we could solve this problem by just treating GList as a node.  For
example, redefine the G_List class this way:

typedef GList G_Node;
class G_List
{ 
  G_Node* pnode;
...
  G_List(G_Node* pnode) : pnode(pnode)
    { }
...
  G_Node* next() { return pnode->next; }
  G_Node* prev() { return pnode->prev; }
  G_Node* node() { return pnode; }
...
}

This makes it just as easy to traverse lists by doing the following:

   G_List list(glib_glist);
   for (G_Node *lptr = list->node(); lptr != NULL; lptr = lptr->next)
      printf("data: %s\n", lptr->data);

Because you are returning a G_Node, and not a G_List, you don't have to
worry about the G_List being modified or anything.

Just my $.02

---
Matt Perry [guy@mikepery.linuxos.org]

QOTD:	I looked out my window, and saw Kyle Pettys' car upside down,
	then I thought 'One of us is in real trouble'.
		-- Davey Allison, on a 150 m.p.h. crash
---