Re: [boost] [any] interest in boost::variant style visitors for boost::any?

From: Eric Friedman (ebf_at_[hidden])
Date: 2007-01-02 03:53:44

Korcan,

Regarding visitation for boost::any, I did some work a long while ago in 
the Boost Sandbox:

http://boost-sandbox.cvs.sourceforge.net/boost-sandbox/boost-sandbox/boost/any.hpp

http://boost-sandbox.cvs.sourceforge.net/boost-sandbox/boost-sandbox/boost/visitor/

I haven't looked at any of this in a while though.

Also, in case you are interested, there is the more experimental 
application of visitation in the form of a "switch" construct:

http://boost-sandbox.cvs.sourceforge.net/boost-sandbox/boost-sandbox/boost/type_switch.hpp

Eric

Korcan Hussein wrote:
> I propose 3 changes/additions made to boost::any:
> 
> 1. Support for custom allocator types.
> 
> 2. Support for in-place factories.
> 
> 3. Last but not least boost::variant style visitors.
> 
> I'll elaborate on the last one, i've written primarily support for 
> boost::variant style visitors for boost::any. The method is based on the 
> acyclic visitor pattern and works as follows:
> 
> struct printer_fn : boost::dynamic_visitor<int, std::string> {
> 
>     void operator()(int) const { std::cout << "int\n" }
>     void operator(const std::string&) cosnt { std::cout << "string\n" }
> 
> } const printer;
> 
> ......
> 
> boost::any a  = 1;
> 
> boost::apply_visitor(a, printer);
> 
> a = std::string();
> 
> boost::apply_visitor(a, printer);
> 
> I'm looking to also provide the ability to extend their visitors (and 
> override if need be) to support more types as well as provide "catch-all" 
> (i.e (const) boost::any&) implementation which defaults to throwing an 
> exception. I also want this to be constant-correct in the way of 
> const_iterator and iterator, i need to look into this carefully since there 
> are 4-cases to deal with (instead of 2).
> 
> Is there any interest for these changes/additions?
> 
> Thanks.
> Korcan Hussein.
> 
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