我发现了这个https://gist.github.com/2945472,但我需要一个不依赖于c ++ 11的实现。我尝试将其转换为仅使用提升,但我遇到了一些麻烦。
以下是我提出的建议:
#include <boost/any.hpp>
#include <boost/function.hpp>
#include <boost/bind.hpp>
#include <boost/lambda/lambda.hpp>
#include <boost/unordered_map.hpp>
struct type_info_hash {
std::size_t operator()(std::type_info const & t) const {
return t.hash_code();
}
};
struct equal_ref {
template <typename T> bool operator()(boost::reference_wrapper<T> a,boost::reference_wrapper<T> b) const {
return a.get() == b.get();
}
};
struct any_visitor {
boost::unordered_map<boost::reference_wrapper<std::type_info const>, boost::function<void(boost::any&)>, type_info_hash, equal_ref> fs;
template <typename T> void insert_visitor(boost::function<void(T)> f) {
try {
fs.insert(std::make_pair(boost::ref(typeid(T)), boost::bind(f, boost::any_cast<T>(boost::lambda::_1))));
} catch (boost::bad_any_cast& e) {
std::cout << e.what() << std::endl;
}
}
bool operator()(boost::any & x) {
boost::unordered_map<boost::reference_wrapper<std::type_info const>, boost::function<void(boost::any&)>, type_info_hash, equal_ref>::iterator it = fs.find(boost::ref(x.type()));
if (it != fs.end()) {
it->second(x);
return true;
} else {
return false;
}
}
};
struct abc {};
void fa(int i) { std::cout << "fa(" << i << ")" << std::endl; }
void fb(abc) { std::cout << "fb(abc())" << std::endl; }
int main() {
any_visitor f;
f.insert_visitor<int>(fa);
f.insert_visitor<abc>(fb);
std::vector<boost::any> xs;
xs.push_back(1);
xs.push_back(abc());
xs.push_back(1.5);
for (auto & x : xs) {
if (!f(x)) std::cout << "no visitor registered" << std::endl;
}
}
插入地图时我收到了bad_any_cast。不应该只通过it-&gt; second(x)来调用any_cast吗?我做错了什么?
答案 0 :(得分:3)
您无法将_1
强制转换为T
(在绑定表达式时)。
你需要一个懒惰的演员。也许定义一个函数并使用嵌套的绑定表达式,或者使用Boost Phoenix和一个自定义的any_cast
actor。
这是嵌套绑定方法:
#include <boost/any.hpp>
#include <boost/function.hpp>
#include <boost/bind.hpp>
#include <boost/lambda/lambda.hpp>
#include <boost/unordered_map.hpp>
struct type_info_hash {
std::size_t operator()(std::type_info const & t) const {
return 42; // t.hash_code();
}
};
struct equal_ref {
template <typename T> bool operator()(boost::reference_wrapper<T> a,boost::reference_wrapper<T> b) const {
return a.get() == b.get();
}
};
struct any_visitor {
boost::unordered_map<boost::reference_wrapper<std::type_info const>, boost::function<void(boost::any&)>, type_info_hash, equal_ref> fs;
template <typename T> static T any_cast_f(boost::any& any) { return boost::any_cast<T>(any); }
template <typename T> void insert_visitor(boost::function<void(T)> f) {
try {
fs.insert(std::make_pair(boost::ref(typeid(T)), boost::bind(f, boost::bind(any_cast_f<T>, boost::lambda::_1))));
} catch (boost::bad_any_cast& e) {
std::cout << e.what() << std::endl;
}
}
bool operator()(boost::any & x) {
boost::unordered_map<boost::reference_wrapper<std::type_info const>, boost::function<void(boost::any&)>, type_info_hash, equal_ref>::iterator it = fs.find(boost::ref(x.type()));
if (it != fs.end()) {
it->second(x);
return true;
} else {
return false;
}
}
};
struct abc {};
void fa(int i) { std::cout << "fa(" << i << ")" << std::endl; }
void fb(abc) { std::cout << "fb(abc())" << std::endl; }
int main() {
any_visitor f;
f.insert_visitor<int>(fa);
f.insert_visitor<abc>(fb);
std::vector<boost::any> xs;
xs.push_back(1);
xs.push_back(abc());
xs.push_back(1.5);
for (auto it=xs.begin(); it!=xs.end(); ++it)
if (!f(*it)) std::cout << "no visitor registered" << std::endl;
}
打印输出:
fa(1)
fb(abc())
no visitor registered
答案 1 :(得分:1)
尝试使用extendable any https://sourceforge.net/projects/extendableany/?source=directory
struct f_method
{
typedef void (boost::mpl::_1::* signature) () const;
template <typename T>
struct wrapper
: public T
{
void f() const
{
return this->call(f_method());
}
};
struct implementation
{
void operator() (int i) const
{
std::cout << "fa(" << i << ")" << std::endl;
}
void operator() (abc) const
{
std::cout << "fb(abc())" << std::endl;
}
template <typename T>
void operator() (const T& t) const
{
std::cout << "Errr" << std::endl;
}
};
};
typedef xany<boost::mpl::list<f_method> > any;
int main() {
std::vector<any> xs;
xs.push_back(1);
xs.push_back(abc());
xs.push_back(1.5);
for (auto it=xs.begin(); it!=xs.end(); ++it)
(*it).f();
}