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

On Fri, Aug 16, 2013 at 5:21 PM, Santiago Tapia wrote:

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Date: Tue, 13 Aug 2013 23:33:25 +0400 From: Andrey Semashev

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- The container classifier is _not_ a sequence.

Why? Is this intentional?

Both intentional and accidental, because I want to allocate objects contiguously in memory I have to store them in a collection of vectors, the container is not a sequence but a collection of sequences, one sequence for every class in the classifier. I will implement a sequence, but later.

The storage strategy does not mandate the interface of the container. unordered_set/map are implemented as a number of buckets (i.e. single-linked lists), yet they provide sequence interface with an additional ability to iterate within a single bucket. I don't see why a similar approach couldn't be taken in your container.

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All in all the basic idea looks interesting, although I'm not sure about the particular classifier container. It looks very specific to me, the same functionality could be achieved with a multimap or unordered_multimap of polymorphic elements.

...or I should have said "multiset or unordered_multiset".

As far as I know it is not possible to get a multimap of a pure abstract class, therefore, for example, you can not use a multimap or multiset<shape> but you can use a classifier<shape> to store triangles, squares, or any derived class. I plan to implement an associate container later, thus you could have classifier and you could look for an object in the classifier using a key.

You can't create std::multiset<shape> but you can create boost::intrusive::multiset<shape>. The reason for that is that std::multiset attempts to allocate storage for shape, while boost::intrusive::multiset doesn't, leaving this to the user. This allows you to insert any objects derived from shape to the single boost::intrusive::multiset and work with this container pretty much the same way you would with std::multiset. You can even insert the very same object in multiple containers if you need to. I recommend you to have a look at Boost.Intrusive, it is a truly amazing library.