Boost.DynamicAny

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Boost.DynamicAny

Boost.DynamicAny is a vairant on Boost.Any which provides more flexible dynamic casting of the underlying type. Whereas retreiving a value from Boost.Any requires that you know the exact type stored within the Any, Boost.DynamicAny allows you to dynamically cast to either any base of the held type.

Boost.DynamicAny passes all of the same unit tests as Boost.Any, but additionally supports the following test:

#include <boost/dynamic_any.hpp>

using boost::dynamic_any_cast;
struct base 
{
    int a;
};

struct base1 
{
    int a1;
};

struct derived : base, base1
{
    int b;
};

struct other {};

void test_dynamic_cast()
{
    derived d;
    dynamic_any a(d);
    derived &                ra  = dynamic_any_cast<derived&>(a);
    base &                   b   = dynamic_any_cast<base&>(a);
    base1 &                  b1  = dynamic_any_cast<base1&>(a);
    const base1 &            cb1 = dynamic_any_cast<const base1&>(a);

    TEST_CHECK_THROW(
        dynamic_any_cast<other&>(a),
        bad_dynamic_any_cast,
        "dynamic_any_cast to incorrect reference type");
}

boost::any_ref

The boost::any_ref class provides a generic reference that automatically casts to reference types. You can also get a pointer to the object and have it return NULL if the type is wrong.

This class is supposed to be a type-safe alternative to void*, typesafety comes at the cost of dynamic_cast<>.

#include <boost/any_ref.hpp>

using boost::any_ref;

void times2( double& v ) { v*=2; }
void print( const double& v ) { std::cerr<<v<<std::endl; }

void test() {
    double          x = 5.5;
    any_ref         r = x;
    times2(r);
    print(r);
    BOOST_ASSERT( x == 11 );

    const double cx = 22;
    any_ref      cr = x;
    print(cr); // OK

    // cannot cast from const double& to double&
    TEST_CHECK_THROW(
        times2(cr),
        bad_any_ref_cast,
        "any_ref_cast to incorrect reference type");
}

Notice

This library is not part of the official Boost C++ library, but
is written, to the best of my ability, to follow the best practices
established by the Boost community and with the hope of being 
considered for inclusion with a future Boost release.