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Last updated 2/12/09 at 12:01 am PST
Cripes! 2.0 -- See the Class Layout
Arenamatic Code w/ cConsole  |   Twisol
Member since: 9/11/2005 From: Los Angeles | 
Posted - 8/13/2009 4:36:59 AM | Ah, me. How easily I get distracted, enticed by the thought of "Oh, that would be cool", or "I wonder if I can do this". The first thing I need to make sure I understand, right now, is that for pity's sake, I'm not trying to write a full-featured C++/Lua binding! 
With that out of the way, I may as well explain what I've done so far (and ultimately scrapped because I can do without it)... You've seen my methods-only object binding from my last post. I may keep that at least. However, you may also remember how I wanted to be able to bind variables, too. I did some experimenting with it, and in the end it did work, but it kills one particular assumption of Lua: variables are dynamically typed. Assigning a string to what once held an integer is acceptable. Not so with my variable binding, and there's no good way around it. Shall I explain? Why not.
All of Lua's lua_push* functions push the value of the variable you pass, not a reference to one. This is a good thing for plenty of reasons, but it also means you need to do some extra work to bind a variable. The only option you have is to store a pointer to the variable as a userdatum. Userdata in Lua have no inherent properties, though; metatables are applied to make them more interesting.
Unfortunately, when you access a Lua variable, the variable itself isn't told about this. It's the metamethods of its [i]parent[/it] container that are notified instead. Specifically, __newindex (for setting) and __index (for getting). So the parent container needs to have these metamethods. It also needs some way to tell if the resource you're asking for is a bound variable and not some other kind of userdatum (or not even userdata at all), namely by checking the userdatum's metatable.
And even after all that, there needs to be some way to actually get/set that variable. These functions are implemented in the C side of things, and called with __index/__setindex are sure that it's a bound C variable that you're trying to get at. The final problem here is that C variables are strongly typed. Passing a string in where the bound variable expects an int, no, you'll get an error. And that's not expected behavior for Lua by any means. At this point I threw in the towel. If I'm implementing get/set methods for these variables, why do I bother at all? I can just bind methods using the approach from my last post and get the same effect, with less hair loss!
I probably rambled a bit there, but it's 2am, so I can't really expect much better of myself. Suffice to say, I can implement the snippet of goal code I gave in my last post in pure C binding rather than doing any C++ object stuff. Maybe I should if it's such a hassle. But what can I say? I like my OO. 
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