Re: [Boost-users] multi-index container: a more general basic usage example 1

Hi Alexander, Alexander Schuh writes:

Hi, in Example 1 there is a structure:

struct employee{ int id; std::string name; int age; … };

Is it possible to create automatically

A) container with id as an index

B) a view with name as index

C) a view with age as index ?

For this example it is easy to create the containers and views by hand but I plan to use at least 10 structures with many dimensions.

For some containers I also need hash_indices - so there is really a lot of similar code, which I don’t want to have.

As C++ lacks reflection facilities, you cannot really get much shorter a specification of the container than it is shown in the example. With a little of preprocessor machinery, it is possible to specify the containers a little more compactly: DEFINE_MULTI_INDEX_CONTAINER( employee, (ordered_unique,int,id) (ordered_non_unique,std::string,name) (ordered_non_unique,int,age) ) With the aid of Boost.Preprocessor, it shouldn't be too hard to implement the DEFINE_MULTI_INDEX_CONTAINER macro so that it expands to the definition in Example 1. Drop me a line if you are interested in this and need assistance crafting such a macro.

Also I want to provide iterators or one general (template) iterator for all dimensions. How would you write such a general iterator?

There should be a function that takes for example “employee_name” or “employee_id” as a parameter to query the employee container. It would also be interesting to have a function that creates an iterator based only on the

Information, for example, multi_index::container(1)_index(2).

You'd need some sort of runtime polymorphism to achieve this. Google for "any_iterator", there's a suitable construct in the Adobe Open Source library, and also a similar lib by Doug Gregor (which finally didn't make it into Boost AFAIK.) Combine any_iterator with an appopriate object factory and you'll get what you want, if I understood your goal correctly.

Is there a function that calculates the max. index number of a certain container?

Yep: template<typename MultiIndexContainer> struct num_of_indices: boost::mpl::size< typename MultiIndexContainer::index_type_list

{}; (the max index number is just one less than num_of_indices.)

Thank you very much,

Alex Schuh

You're welcome; thank you for using Boost.MultiIndex, Joaquín M López Muñoz Telefónica, Investigación y Desarollo