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

Subject: Re: [boost] [cpo-proposal] presentation of the idea
From: Larry Evans (cppljevans_at_[hidden])
Date: 2013-08-13 08:42:03

On 08/12/13 19:07, Santiago Tapia wrote:
> Hi everyone,
> 
> I would like to make a proposal for a new library. I only have a draft
> without documentation but I would like to know people’s opinion
> about the idea before making a formal proposal.
> 
> The library will be named CPO (containers for polymorphic objects)
> and it will provide containers to store dynamic allocated objects from
> a class hierarchy. I have drafted one container and I have two more
>  in process. The cpo library could be an alternative solution for
> boost pointer container library or some other solutions that use pointers.
> In order to understand the idea, I think that the following example of the
> use of the library might be better than a long explanation:
> 
> #include <boost/cpo/classifier.hpp>
> #include <iostream>
> 
> using namespace boost::cpo;
> 
> class base
> {
> public:
>   virtual int do_something(int a) const = 0;
> };
> 
> class derived_A : public base
> {
> public:
>   derived_A(int b) : data(b) {}
>   virtual int do_something(int a) const
>   {
>      return a + data;
>   }
> protected:
>   int data;
> };
> 
> class derived_B : public base
> {
> public:
>   derived_B(int b) : data(b) {}
>   virtual int do_something(int a) const
>   {
>      return a - data;
>   }
> protected:
>   int data;
> };
> 
> int main(int argc, char** argv)
> {
>   classifier<base, std::allocator> collection;
> 
>   collection.insert( derived_A(21) );
>   collection.insert( derived_B(40) );
> 
>   classifier<base, std::allocator>::iterator i, e = collection.end();
> 
>   for ( i = collection.begin(); i != e; ++i )
>   {
>     const base& x = *i;
>     std::cout << x.do_something(6) << std::endl;
>   }
> 
>   return 0;
> }
[snip]
Hi Santiago,

What if the class hierarchy is used to model a graph that
contains cycles.  For example, something like a spirit grammar
where a non-terminal on the rhs of a non-terminals definition?
Wouldn't this require some sort of smart pointer or other
garbage collection method with the ability to collect cycles?

-regards,
Larry