Boost类型擦除对象转回原类型触发boost::bad_any_cast问题求助

Ah, I see the issue here! You're mixing up two distinct Boost type erasure tools—boost::any and boost::type_erasure::any—and trying to use the wrong casting function with the latter. The boost::any_cast is designed exclusively for the general-purpose boost::any type, not the concept-driven any from Boost.TypeErasure. That's why you're hitting the runtime exception.

Here's the Fix #

You need to use boost::type_erasure::any_cast instead, which is purpose-built for the concept-based any you're using. First, make sure to include the required header for this function:

#include <boost/type_erasure/any_cast.hpp>

Revised Working Code #

Here's your code updated with the correct casting approach:

#include <boost/type_erasure/member.hpp>
#include <boost/type_erasure/any.hpp>
#include <boost/type_erasure/any_cast.hpp> // Critical missing header!
#include <iostream>

BOOST_TYPE_ERASURE_MEMBER((has_x), x, 0)
namespace bte = boost::type_erasure;
using xConcept = boost::mpl::vector<has_x <float(), bte::_self> , bte::copy_constructible<>, bte::relaxed>;
using AnyXobject = bte::any<xConcept, bte::_self>;

struct xThing{
 float x(){ return 4.; }
 float y(){ return 5.; }
};

int main(){
 xThing i;
 AnyXobject xconc(i);

 std::cout << xconc.x() << std::endl; // This still works as expected

 // Use the correct any_cast from boost::type_erasure
 auto j = bte::any_cast<xThing>(xconc); 
 std::cout << j.y() << std::endl; // Now you can access the original type's y() method

 // For safer, non-throwing conversion (returns nullptr on failure):
 if (auto j_ptr = bte::any_cast<xThing>(&xconc)) {
     std::cout << j_ptr->y() << std::endl;
 }

 return 0;
}

Key Context to Remember #

• boost::any is a simple, "catch-all" type erasure for any copyable type, while boost::type_erasure::any is a more flexible, concept-driven system that lets you define exactly which operations the erased type supports.
• Their casting functions are not interchangeable—always match the any_cast to the type of any you're using.
• The non-throwing pointer version of bte::any_cast is great for cases where you're uncertain about the underlying type and want to avoid runtime exceptions.

内容的提问来源于stack exchange，提问作者the_toast