Clear cutting

by David Humphrey

I'm terrible at enjoying a success, because as soon as I get something to work, I lift my gaze to the next horizon. Previously I got close to finding all possible concrete types for:

privatePrevAccessible->SetParent(this);

However, I had cheated by only building the parts of the tree that I knew contained what I wanted. I also got back the type itself, so B+. My trouble was that I needed a way to get at multiple levels of inheritance for a type, in order to find the right method. To recap, privatePrevAccessible is really nsPIAccessible, and I need to know all of the concrete types that this could be. Working backwards, there are two: nsAccessible and nsHTMLListBulletAccessible.

nsAccessible is pretty easy, since nsPIAccessible is a direct base class. However, nsHTMLListBulletAccessible is an nsPIAccessible only by marriage:

nsHTMLListBulletAccessible : nsHyperTextAccessibleWrap : nsHyperTextAccessible : nsAccessibleWrap : nsAccessible : nsPIAccessible

My trouble was that I was doing things the proper way, and carefully recreating the entire inheritance tree recursively in the database. This made it difficult (I won't say impossible, but I want to) to get from nsHTMLListBulletAccessible to nsPIAccessible without working way too hard in SQL.

Being a fan of the "worse is better" philosophy of programming, I decided that I wasn't smart enough to solve the problem as given. Instead, I decided to flatten the inheritance tree for each type, and simply record relation from concrete class to base classes, but not retain the structure--I don't actually need the authentic view of the class hierarchy [ed. I'm sure this will come back to haunt me, but I'm happy right now]. And it worked! My db still needs some pruning, and the SQL needs to be optimized, but I can quickly and easily go from nsPIAccessible->SetParent(nsIAccessible*) to nsAccessible->SetParent(nsIAccessible*) and nsHTMLListBulletAccessible->SetParent(nsIAcessible*) in one step. Lesson: when you can't find something in a forest, cut down the trees [ed. this advice should not be applied outside the computing space without more study].

So as I said at the beginning, I don't know when to stop and smell the roses. As soon as I got this working, I took a look at the source lines where deyhdra was pointing me for both methods:

  • NS_DECL_NSPIACCESSIBLE
  • NS_IMETHOD SetParent(nsIAccessible *aParentAccessible);
    Not exactly what I was hoping for. After chatting with Dave a bit last night on irc, I'm going to see if I can exploit process_function() and .methodOf to separate decls and defs. Can you spell F-U-N?

If I stop for a minute to think about everything I still need to do I get totally discouraged, so I'm trying to follow my own advice and make baby steps every day. Pretty soon I'm thinking I'd better do a prototype web front-end so you can play along at home.