Rozental, Gennadiy wrote:

BTW, while we are on topic. Your implementation uses code like this

struct any_t {...}; template<typename T> struct static_any_t : any_t {...}

template<typename T> static_any_t<T> foo(...);

If( any_t const& ref = foo() ) { // here you are using ref }

Is it indeed allowed in standard and ref is valid reference to temp?

Gennadiy.

Yup, that's perfectly OK. Binding a temporary to a const reference extends the lifetime of the temporary. And if it's a const reference to a base, the whole derived object sticks around, not just the base sub-object (no slicing). In addition, if the derived object has a non-trivial destructor, it will get called when the const reference to base goes out of scope /even if base has a non-virtual destructor/. It's like magic. But not really. :) The real magic in BOOST_FOREACH is how to recover the lost type information without virtuals, dynamic casts or RTTI. And that's with sneaky template tricks and static_cast. -- Eric Niebler Boost Consulting www.boost-consulting.com