Re: [boost] [cpo-proposal] presentation of the idea

Subject: Re: [boost] [cpo-proposal] presentation of the idea
From: Thorsten Ottosen (thorsten.ottosen_at_[hidden])
Date: 2013-08-28 02:57:49

On 28-08-2013 06:51, Gottlob Frege wrote:
> <snip> big thread about polymorphic container ... </snip>
>
> I hope I didn't miss anything in the thread.  If I'm repeating something,
> sorry.
>
>
> I don't think we want or need to limit what we put into the container.
> Neither by forcing certain virtual functions onto the base class, nor by
> limiting what the contained types can and can't do (like have pointers to
> themselves and do funky things in their copy/move constructors).
>
> When push_back<Triangle> is called, we create an instance of an
> ItemHandler<Triangle> class, that derives from BaseItemHandler, and
> implements copy/move virtually. ie type-erasure.  ItemHandler<Triangle>
> knows how to move/copy Triangles.  It is not Triangle's job!
>
> We put the ItemHandler<Triangle> in a map<RTTI, BaseItemHandler*>.

[Thorsten:]

This is a bad idea IMO. The point of such a container is to provide
as little fragmentation of the heap as possible, to get better
locality of data (when the data consists of polymorphic objetcs).
With

  std::vector<int>

we get great locality. We don't yet have such an alternative for
polymorphic objects.

kind regards

-Thorsten