Applying a boost::mpl::list to the template parameter of a type
I have a class that requires a boost::variant containing shared pointers to various types as follows:
template <typename ToySharedPtrVariant, typename ColorSharedPtrVariant>
class ToyPicker {
typedef std::pair<
ToySharedPtrVariant,
ColorSharedPtrVariant
> toyAndColorPair;
typedef std::map<
std::string,
std::vector<
toyAndColoPair
>
> stringToToyColorPairMap;
// ... methods that use the defined types...
}
This class currently requires template parameters of the following form to compile:
ToyPicker<
bo开发者_运维知识库ost::variant<
boost::shared_ptr<ToyModel>
>,
boost::variant<
boost::shared_ptr<BlueToy>,
boost::shared_ptr<RedToy>,
boost::shared_ptr<GreenToy>
>
> toyPicker;
How do I use an mpl list so that I can allow the following much simpler definition for users, then convert it into the example format above inside my class implementation?
ToyPicker<
boost::mpl::list<
ToyModel
>,
boost::mpl::list<
BlueToy,
RedToy,
GreenToy
>
> toyPicker;
Using boost::mpl::transform in conjunction with boost::make_variant_over does the trick :
#include <boost/mpl/list.hpp>
#include <boost/mpl/transform.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/variant/variant.hpp>
template<class T>
struct add_shared_pointer
{
typedef boost::shared_ptr<T> type;
};
template<class Seq>
struct shared_ptr_variant
{
typedef typename boost::make_variant_over<
typename boost::mpl::transform<
Seq, add_shared_pointer<boost::mpl::_1>
>::type
>::type type;
};
Look at boost::make_variant_over it does what you need.
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