Boost C++ Libraries

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Function dynamic_any_cast

boost::type_erasure::dynamic_any_cast

Synopsis

// In header: <boost/type_erasure/dynamic_any_cast.hpp>


template<typename R, typename Any> R dynamic_any_cast(Any && arg);
template<typename R, typename Any, typename Map> 
  R dynamic_any_cast(Any && arg, const static_binding< Map > &);

Description

Downcasts or crosscasts an any.

The single argument form can only be used when R uses a single non-deduced placeholder.

Example:

// Assume that typeid_<>, copy_constructible<>, and incrementable<>
// have all been registered for int.
any<mpl::vector<typeid_<>, copy_constructible<> > > x(1);
typedef any<
    mpl::vector<
        typeid_<>,
        copy_constructible<>,
        incrementable<>
    >
> incrementable_any;
auto y = dynamic_any_cast<incrementable_any>(x);
++y;
assert(any_cast<int>(y) == 2);

Requires:	`R` and `Any` must both be specializations of any.
Requires:	PlaceholderMap must be an MPL map with a key for every non-deduced placeholder used by R. The value associated with each key should be the corresponding placeholder in Any.
Requires:	The concept of Any must include typeid_, for every placeholder which is used by R.
Throws:	bad_any_cast if the concepts used by R were not previously registered via a call to register_binding.