Re: [boost] [pointer container] Wishlist: Iterating through nullable vectors and compiler firewalls

From: Andrew Hain (andrew.hain_at_[hidden])
Date: 2008-08-31 09:52:23

Thorsten Ottosen <thorsten.ottosen <at> dezide.com> writes:

> 
> Andrew Hain skrev:
> > Two quick queries.
> > 
> > Would it make sense to have the iterator increment and decrement operators 
and 
> > begin() member function of ptr_vector< nullable<> > skip missing records so 
> > that applications have no need to check?
> 
> Well, it is always a design trade-off. If we did that, then people who 
> need to know the index of the null value is in trouble.
> 
> I do think it would make sense to add some utility iterator/range:
> 
> boost::ptr_vector<T> vec;
> ...
> BOOST_FOREACH( T& e, boost::filter_nulls(vec) )
> 
> or something. I'm open to naming ideas 

Something like that could be useful.

> 
> > What is stopping pointer container classes from being used with opaque 
types 
> > as a compilation firewall?
> 
> Can you be more specific? I have some trouble knowing the precise problem.
> 

I have been looking at replacing a homebrewed template class with ptr_vector. 
The homebrewed template supports opaque classes with a nasty trick that only 
allows the template to be used with types known to its definition; this is one 
of the reasons I am trying to replace it. During my test I created a clone 
template that calls a Clone() member function in each class and I got compiler 
errors when the class arguments to ptr_vector are undefined. Would opaque 
classes work with a separate out-of-line definition of each class?

> Thanks
> 
> -Thorsten
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