boost::openmethod::inplace_vptr_base
Embed a v‐table pointer in a class.
Synopsis
Declared in <boost/openmethod/inplace_vptr.hpp>
template<
class Class,
class Registry = boost::openmethod::default_registry>
class inplace_vptr_base
: protected /* implementation-defined */Protected Member Functions
Name |
Description |
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Set the vptr to |
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Set the vptr to |
Description
inplace_vptr_base is a CRTP mixin that embeds a v‐table pointer at the root of a class hierarchy. It also declares a boost_openmethod_vptr free function that returns the v‐table pointer stored in the object.
inplace_vptr_base registers the class in Registry. It is not necessary to register the class with use_class or BOOST_OPENMETHOD_REGISTER
The v‐table pointer is obtained directly from the Registry's static_vptr variable. No hashing is involved. If all the classes in Registry inherit from inplace_vptr_base, the registry needs not have a policies::vptr policy, nor any policy it depends on (like policies::type_hash).
If Registry contains the has_indirect_vptr policy, the v‐table pointer is stored as a pointer to a pointer, and remains valid after a call to initialize.
The default value of Registry can be changed by defining BOOST_OPENMETHOD_DEFAULT_REGISTRY
Example
#include <boost/openmethod.hpp>
#include <boost/openmethod/inplace_vptr.hpp>
#include <boost/openmethod/initialize.hpp>
using namespace boost::openmethod;
struct Animal : inplace_vptr_base<Animal> {};
struct Cat : Animal, inplace_vptr_derived<Cat, Animal> {};
struct Dog : Animal, inplace_vptr_derived<Dog, Animal> {};
BOOST_OPENMETHOD(
poke, (virtual_<Animal&> animal, std::ostream& os), void);
BOOST_OPENMETHOD_OVERRIDE(poke, (Cat&, std::ostream& os), void) {
os << "hiss\n";
}
BOOST_OPENMETHOD_OVERRIDE(poke, (Dog&, std::ostream& os), void) {
os << "bark\n";
}
int main() {
initialize();
std::unique_ptr<Animal> a = std::make_unique<Cat>();
std::unique_ptr<Animal> b = std::make_unique<Dog>();
poke(*a, std::cout); // hiss
poke(*b, std::cout); // bark
return 0;
}