[cfe-commits] r60597 - in /cfe/trunk: include/clang/AST/ include/clang/Basic/ include/clang/Parse/ lib/AST/ lib/CodeGen/ lib/Parse/ lib/Sema/ test/Parser/

[Sebastian Redl]

Douglas Gregor wrote:
> On Dec 5, 2008, at 8:01 PM, Sebastian Redl wrote:
>
>> Looks pretty good. I'm a bit worried that this approach means that 
>> pretty much every bit of Sema code that does some kind of type or 
>> capability checking has to be aware of template types and defer their 
>> checking. Is this correct? If so, is there any way we can avoid it? 
>> I'm envisioning bugs en masse that only appear in template code.
>
> This is absolutely correct. Before checking whether a particular 
> expression or declaration is valid, we will need to check whether its 
> parts are dependent (dependent types, type-dependent expressions, 
> value-dependent expressions, etc.).
OK, at the very least, we need a simple way to do this 
(Expr::isDependent()). But undoubtedly you're planning that already.
> Frankly, I don't think there's any way around it.
I was afraid of that. And I'm also afraid that we'll have yet another 
case when we get concepts, because I don't think that constrained type 
parameters are quite the same as concrete types. Or are they?
> Getting some level of template support into the compiler early perhaps 
> means that we can be conscientious about adding template support for 
> something as soon as we add the non-template support for it. We should 
> try to enforce this through the type system.
Hmm ...

Anyway, it'll also need restructuring so that all the checkers can be 
called from the template instantiator. We definitely have a lot of work 
ahead.
>
> The dependent-types computation will be coming later today.
3 and a half hours left of today where I am, but I'm looking forward to 
it. ;-)

By the way, how does GCC do this stuff?

Sebastian