visitor.hpp

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#pragma once
 
#include <ext/utility>
 
#include <alib/tuple>
 
namespace core {
 
template < class ReturnType, class Visitor, class ... Params >
class VisitorContextAux {
    typename std::aligned_storage < sizeof ( ReturnType ), alignof ( ReturnType ) >::type result;
 
    ext::tuple < Params ... > m_params;
 
public:
    VisitorContextAux ( Params && ... params ) : m_params ( std::forward < Params > ( params ) ... ) {
    }
 
    template < class Inherit, size_t ... Indexes >
    void call ( const Inherit & inherit, std::index_sequence < Indexes ... > ) {
        new ( & result ) ReturnType ( Visitor::visit ( inherit, std::forward < Params > ( std::get < Indexes > ( m_params ) ) ... ) );
    }
 
    template < class Inherit, size_t ... Indexes >
    void call ( Inherit & inherit, std::index_sequence < Indexes ... > ) {
        new ( & result ) ReturnType ( Visitor::visit ( inherit, std::forward < Params > ( std::get < Indexes > ( m_params ) ) ... ) );
    }
 
    template < class Inherit, size_t ... Indexes >
    void call ( Inherit && inherit, std::index_sequence < Indexes ... > ) {
        new ( & result ) ReturnType ( Visitor::visit ( std::forward < Inherit > ( inherit ), std::forward < Params > ( std::get < Indexes > ( m_params ) ) ... ) );
    }
 
    ReturnType getResult ( ) {
        ReturnType res = reinterpret_cast < ReturnType && > ( result );
 
         // reinterpret_cast < ReturnType * > ( & result )->~ReturnType ( ); // not needed to delete; data gets moved from on previous line
        return res;
    }
 
};
 
template < class Visitor, class ... Params >
class VisitorContextAux < void, Visitor, Params ... > {
 
    ext::tuple < Params ... > m_params;
 
public:
    VisitorContextAux ( Params && ... params ) : m_params ( std::forward < Params > ( params ) ... ) {
    }
 
    template < class Inherit, size_t ... Indexes >
    void call ( const Inherit & inherit, std::index_sequence < Indexes ... > ) {
        Visitor::visit ( inherit, std::forward < Params > ( std::get < Indexes > ( m_params ) ) ... );
    }
 
    template < class Inherit, size_t ... Indexes >
    void call ( Inherit & inherit, std::index_sequence < Indexes ... > ) {
        Visitor::visit ( inherit, std::forward < Params > ( std::get < Indexes > ( m_params ) ) ... );
    }
 
    template < class Inherit, size_t ... Indexes >
    void call ( Inherit && inherit, std::index_sequence < Indexes ... > ) {
        Visitor::visit ( std::forward < Inherit > ( inherit ), std::forward < Params > ( std::get < Indexes > ( m_params ) ) ... );
    }
 
    void getResult ( ) {
    }
 
};
 
} /* namespace core */