Christian, On 9/7/07, Christian Holmquist <c.holmquist@gmail.com> wrote:
Is there any visitor mechanism somewhere in boost that allows one to introspect the contained type of a boost::any? I've been using boost::variant frequently and I love the way its visitor works, but it's not always practical to know all possible types at compile time (library dependencies, compilation time etc..). [snip] Does anyone else have a use for this, or have another solution at hand?
Some long time back I had added support into Boost.Any for visitation: http://boost-sandbox.cvs.sourceforge.net/boost-sandbox/boost-sandbox/boost/a... http://boost-sandbox.cvs.sourceforge.net/boost-sandbox/boost-sandbox/libs/an... Basically, the interface is as seen in the `test_dynamic_visit` test case: class my_visitor : public boost::dynamic_visitor_base, public boost::dynamic_visitor_interface<T1>, ..., public boost::dynamic_visitor_interface<TN> { ... public: /*override*/ void visit(T1&); ... /*override*/ void visit(TN&); }; and then an instance of the visitor may be passed to a boost::any: boost::any a = ...; my_visitor v; boost::apply_visitor(v, a); Of course this assumes (parts of) the Boost.Visitor library, also in the sandbox. In any case, something based on this idea might be another alternative to what you're proposing. Eric