Warp wrote:
>   I still can't comprehend what's so bad in the compiler doing the check
> that you don't access the private members.

If it's actually enforced (as in an error rather than a warning), it makes 
lots of things harder than they need to be, because the running code winds 
up with less information than the compiler had. You're throwing away half 
the work the compiler did once you generate the code, so you wind up with 
lots of boilerplate to enter into code things the compiler already knows.

If it's not enforced (i.e., it's a warning), then I don't see it as an 
improvement over a naming convention. People don't accidentally use x._y in 
their python code any more than they accidentally name something 
__builtin_printf in their C code. In CLOS, you actually have to go read the 
source code of the implementation of the class to see what member variables 
you can access, so it's not like you don't know you're violating encapsulation.

If it's *really* enforced (as in you actually can't get to private 
variables), it lets you do things like prove your program is correct and 
lets you do things like know you've got a bug in your module when an 
instance variable winds up with the wrong value.

If it's half-enforced, as in the compiler complains and won't compile the 
code, but there's ways to get around it anyway (on purpose or by mistake), 
then it's IMO the worst of all possible worlds. You'll spend hours or days 
trying to debug code that's already right because the client is convinced 
the other code they've written is bugfree and it's easier to blame you than 
to find the wild pointer in their own code. The whole idea of class 
invariants goes out the window.

Incidentally, I see little wrong with breaking encapsulation if you maintain 
the invariants. It makes it harder to upgrade in the future without changing 
the client, but that's the price you pay for it. If you can automate the 
access to where it doesn't hurt to change the client, it seems like a 
win-win to me.

-- 
   Darren New, San Diego CA, USA (PST)
   My fortune cookie said, "You will soon be
   unable to read this, even at arm's length."

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