[wwwdocs] Update coding conventions for C++

[Jason Merrill]

On 06/27/2012 08:35 AM, Chiheng Xu wrote:
> dynamic_cast use RTTI, while TREE_CODE are poor man's type info. RTTI
> is better than TREE_CODE. But, If you decide to use RTTI,  TREE_CODE
> become redundant, that means all use of TREE_CODE should be removed,
> sooner or later. Are you prepared for that ?

I wasn't suggesting we would change trees to use inheritance in the 
forseeable future; my point was that RTTI is used in patterns like what 
we already do with trees, so I don't think that using it indicates a 
design problem.

If we were to change trees to use inheritance and virtual functions, 
which seems unlikely to me, then I think it would make sense to use RTTI 
instead of TREE_CODE.

On 06/27/2012 09:02 AM, Richard Guenther wrote:
> RTTI requires more space than TREE_CODE, so it's not universally better.

RTTI requires no additional space in each object, and no space at all 
for classes with no virtual functions.

> To answer, no - we should not enable RTTI (nor exceptions).

The problem with exceptions is that the compiler is not exception-safe. 
  I don't think there's a good reason to prohibit RTTI.  As I said in 
another message, I don't mind turning it off for now, but I don't think 
doing so has much benefit either, since it only affects classes with 
virtual functions.

Jason