Re: [boost] "any" now in CVS

From: Peter Dimov (pdimov_at_[hidden])
Date: 2001-07-05 09:55:38

From: "George A. Heintzelman" <georgeh_at_[hidden]>
[...]
> The second complaint is a little harder to deal with. I often store 
> fairly small objects in the any -- ints, floats, doubles, std::strings. 
> In these cases, the any is a pointer to an object the size of a 
> pointer, and involves unnecessary dynamic memory allocation. I would 
> like to see investigated an any implementation where the type is stored 
> in the object proper, and 'small' objects are likewise stored in the 
> objects. It seems like a no-brainer to store objects up to 
> sizeof(pointer) in the object proper (giving the any a 
> 2*sizeof(pointer) on most implementations), but where to draw the line 
> is probably a question of the specific usage.

It's not exactly a no-brainer because of alignment requirements.

> Finally, I have one suggestion for longer range work. One use of the 
> any-type is in returning values from database queries, where the C++ 
> code doesn't necessarily know what it will get back. In that context, 
> one will often get returned arrays of many objects of a single, unknown 
> type. It seems silly to store the type of these objects repeatedly. 
> Thus, it would be useful to have an any_array type as well, or perhaps 
> an any-adapter for STL containers, though some thought needs to go into 
> how to do that correctly.

I think that you can return a std::vector<T> wrapped in an 'any'.

--
Peter Dimov
Multi Media Ltd.