Re: [boost] Repost (putting together boost::any, mpl::vector, and filter_iterator)

From: Stephen Gross (sgross_at_[hidden])
Date: 2005-09-15 08:36:17

> >I've put together a class called 'AnyVector' for doing type-based 
> >iteration

> >on a vector. The basic idea is that AnyVector wraps a

> >std::vector<boost::any>. The AnyVector lets you iterate across a subset 
> >of

> >the underlying vector by using filter_iterators. The filter iterators, in

> >turn, dereference to the requested type for ease of use. For instance, 
> >you

> >can do the following:

>

> I've done something similar to this in the past, but found it notoriously

> slow to filter on types with boost::any - (on top of this I also added the

> capability to cast into another type, and throw if it was not possible).

>

> Not to disuade you, however, I would really be interested to know if 
> you've

> profiled your code for a mix of types (say 10 or more atomic types).

Nope, I haven't done any profiling... I imagine it doesn't run too quickly 
if you have a large number of a lot of different types. But the tradeof from 
a design perspective is pretty cool (having a single container store all 
sorts of types!).

The other way to design the container (for performance purposes) is to store 
a map<typeinfo, vector<boost::any> >. Any particular vector in the map only 
has boost::any's corresponding to the matching typeinfo. When you want an 
iterator, the container looks like the type requested in the map and returns 
an iterator to the corresponding vector. It works faster, but it's less 
elegant.

--Steve