Re: [boost] [serialization] Inherited objects

From: David Abrahams (dave_at_[hidden])
Date: 2005-10-11 15:39:55

"Robert Ramey" <ramey_at_[hidden]> writes:

> Simon Buchan wrote:
>> Robert Ramey wrote:
>>> Double check that a is polymorphic - that is, that it has at least
>>> one virtual function.  Then get back to us.
>>>
>>> Robert Ramey
>>>>
>>>> I'm guessing that is supposed to be:
>>>>
>>>> main(){
>>>>    ...
>>>>    ar.register_type<derived_one>();
>>>>    ar.register_type<derived_two>();
>>>>    base *b;
>>>>    ar & b;
>>>> }
>>>
>>>
>>> nope, its correct.  This is a little known quirk of C++ syntax.
>>> Your second version won't compile on the most conforming compilers.
>>>
>> Not according to Comeau:
>> "ComeauTest.c", line 16: error: the "template" keyword used for
>>           syntactic disambiguation may only be used within a template
>>
>
> whoops - wrong again.  If ar is a template you need "ar.template" other wise 
> you shouldn't have it.  

Nope, wrong again.  If ar's type X is dependent and "register_type" is a
nested template in X, then you need "ar.template register_type<...>".
Otherwise, you need "ar.register_type<...>"

> From the above code it could be either.  Its really annoying to me
> to have to keep the context and provinence of a variable like "ar"
> in my head while I'm writting.  

Guess what; you don't.  If you had to know whether ar was a template
or not, just think how impossible it would be to write generic code?

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com