我想使用具有不同值类型的多个映射来实现异构存储。我根据值类型索引地图。为此,我使用的是类型列表。这是一个简化的例子。
我的type-list
课程如下所示。
namespace details
{
struct null{};
template<int N, typename E, typename T, typename ... Ts>
struct index : index<N+1, E, Ts...> {};
template<int N, typename E, typename ... Ts>
struct index<N, E, E, Ts...>
{
constexpr static int value = N;
};
template<int N, typename E>
struct index<N, E, null>
{
constexpr static int value = -1;
};
}
template<typename ... Ts>
struct typelist
{
using type = typelist<Ts...>;
template<typename T>
struct index : details::index<0, T, Ts..., details::null> {};
};
以下的存储类实现,一个模板类,其类型为T
。
#include <iostream>
#include <tuple>
#include <typeinfo>
#include <map>
template<typename T>
struct storage_impl
{
//storage_impl(storage_impl const &) = delete;
bool try_getting(int key, T &value)
{
auto search = _storage.find(key);
if(search != _storage.end() )
{
value = search->second;
return true;
}
return false;
}
std::map<int,T> _storage;
};
最后,存储管理器看起来像是,它有几个storage_impl实例,我想根据类型对它们进行索引。
struct storage_manager{
// tuple storing different storage_impls
std::tuple< storage_impl<double> , storage_impl<std::string> > storages { storage_impl<double>{},storage_impl<std::string>{} };
using item_types = typelist<double,std::string>;
storage_manager(){}
~storage_manager(){}
storage_manager(storage_manager const &) = delete;
template<typename T>
bool try_getting(int key, T &value)
{
return std::get<item_types::index<T>::value>(storages).try_getting(key,value);
}
};
int main()
{
storage_manager mgr;
double val1;
std::cout<<mgr.try_getting(123,val1);
}
每件事都有效,直到storage_impl
为copyable
。但我希望storage_impl
为non-copyable
。
如何与我的storage_impl
non-copyable
实现相同的目标。
P.S。 - 不想使用继承。
答案 0 :(得分:0)
以下是我的工作代码,我已经将cache_impls声明为成员变量,并为每种情况声明了专用函数storage_ref
。
我只实现了try_get
,其他功能可以使用storage_ref
实现。
#include <iostream>
#include <tuple>
#include <map>
#include <boost/noncopyable.hpp>
template<typename T>
struct storage_impl : public boost::noncopyable
{
storage_impl(){}
~storage_impl(){}
bool try_getting(int key, T &value)
{
auto search = _storage.find(key);
if(search != _storage.end() )
{
value = search->second;
return true;
}
return false;
}
bool try_setting(int key, T const &value)
{
auto search = _storage.insert(std::make_pair(key,value));
if(search.second == true )
{
return true;
}
return false;
}
bool exists(int key)
{
auto search = _storage.find(key);
if(search != _storage.end() )
{
return true;
}
return false;
}
std::map<int,T> _storage;
};
struct storage_manager : public boost::noncopyable
{
storage_impl<double> double_store;
storage_impl<std::string> string_store;
template<typename T>
struct item_return{ using type = storage_impl<T>; };
template<typename T>
typename item_return<T>::type storage_ref();
template<typename T>
bool try_getting(int key, T &value)
{
return storage_ref<T>().try_getting(key,value);
}
template<typename T>
bool try_setting(int key, T const &value)
{
return storage_ref<T>().try_setting(key,value);
}
template<typename T>
bool exists(int key)
{
return storage_ref<T>().exists(key);
}
storage_manager(){}
~storage_manager(){}
};
//double specialization
template<>
struct storage_manager::item_return<double>{ using type = storage_impl<double>&; };
template<>
inline storage_impl<double>& storage_manager::storage_ref<double>()
{
return double_store;
}
//std::string specialization
template<>
struct storage_manager::item_return<std::string>{ using type = storage_impl<std::string>&; };
template<>
inline storage_impl<std::string>& storage_manager::storage_ref<std::string>()
{
return string_store;
}
int main()
{
storage_manager mgr;
double val1 = 90;
std::cout<<mgr.try_getting(123,val1)<<'\n';
std::cout<<mgr.try_setting(123,val1)<<'\n';
std::cout<<mgr.exists<double>(123)<<'\n';
std::string val2;
std::cout<<mgr.try_getting(123,val2)<<'\n';
}
期待替代品......