Re: [Boost-users] compilation problem and a couple of boost::variant questions

On 07/11/12 13:32, Petros wrote:

Hi, I am trying to write some operator that multiplies two variants, each [snip] First here is the code:

#include using boost::variant;

struct Zero1{ double operator[]( const size_t i ) const { return 0L ; } }; struct One1{ double operator[]( const size_t i ) const { return 1L ; } }; struct Zero2{ double operator[]( const size_t i ) const { return 0L ; } }; struct One2{ double operator[]( const size_t i ) const { return 1L ; } }; struct Vector1{ double operator[]( const size_t i ) const {return double( i ) ; } }; struct Vector2{ double operator[]( const size_t i ) const {return double( 2*i ) ; } }; struct subscript_operator:public boost::static_visitor<double>{ const size_t i_; subscript_operator( const size_t i ):i_(i){}

template<typename _v> double operator()( _v const & v ) const { return v[i] ; } };

template class VariantT :public variant< _V, _Z, _U > { public: typedef typename _Z zero_type ; typedef typename _U unit_type ;

typedef typename VariantT<_V, _Z, _U> self_type ; typedef typename variant< _V, _Z, _U > variant_type ;

template < typename _V> explicit VariantT( _V const & v ) :variant_type(v) {} VariantT() {} VariantT( self_type const & v ) :variant_type(static_cast(v)) {} template < typename _V> VariantT & operator = ( _V const & v ) { *static_cast(this) = static_cast(v); return(*this); } VariantT & operator = ( self_type const & v ) { *static_cast(this) = v; return(*this); }

double operator[]( const size_t i ) const { boost::apply_visitor( subscript_operator(i) , *this ) ; }

bool isZero() const { return which() == 1 ; } bool isUnit() const { return which() == 2 ; }

private: };

template < typename _V1, typename _V2 > class MultVarVar{ public: MultVarVar( _V1 const & v1, _V2 const & v2 ) :v1_(v1),v2_(v2) {} ~MultVarVar() {}

typedef typename _V1::zero_type zero_type ; typedef typename _V1::unit_type unit_type ;

double operator[]( const size_t i ) const { return boost::apply_visitor ( elementwise_visitor( i ), v1, v2 ) ; }

private: _V1 const & v1_ ; _V2 const & v2_ ;

struct elementwise_visitor : public boost::static_visitor< double > { const size_t & i_; public: elementwise_visitor( const size_t & i ) :i_(i) {} template double operator()( _V1 const & v1, _V2 const & v2) const { return v1[i_] * v2[i_] ; } }; };

template < typename _V1, typename _V2 > class MultVarVarResult :public variant, typename MultVarVar<_V1,_V2>::zero_type, typename MultVarVar<_V1,_V2>::unit_type, _V1, _V2 > { public: typedef typename variant< typename MultVarVar<_V1, _V2 > , typename MultVarVar<_V1,_V2>::zero_type, typename MultVarVar<_V1,_V2>::unit_type, _V1, _V2 > variant_type; typedef typename MultVarVarResult<_V1, _V2> self_type ;

typedef typename _V1::zero_type zero_type ; typedef typename _V1::unit_type unit_type ;

template<typename _V> /*explicit*/ MultVarVarResult( _V const & v ) :variant_type(v) {} MultVarVarResult( self_type const & v ) :variant_type(static_cast(v)) {} template < typename _V> MultVarVarResult & operator = ( _V const & v ) { *static_cast(this) = static_cast(v); return(*this); } MultVarVarResult & operator = ( self_type const & v ) { *static_cast(this) = v; return(*this); }

double operator[]( const size_t i ) const { boost::apply_visitor( subscript_operator(i), *this ) ; } private: };

template MultVarVarResult<_V1, _V2> operator * ( _V1 const & v1, _V2 const & v2 ) {

if ( v1.isZero() || v2.isZero() ) return MultVarVarResult<_V1, _V2>( typename MultVarVar<_V1,_V2>::zero_type() ) ; if ( v1.isUnit() ) return MultVarVarResult<_V1, _V2>( v2 ); if ( v2.isUnit() ) return v1 ; else return MultVarVarResult<_V1, _V2>( MultVarVar<_V1, _V2>( v1, v2 ) ) ; }

typedef VariantT< Vector1, Zero1, One1 > Variant1; typedef VariantT< Vector2, Zero2, One2 > Variant2;

int main(){ Variant1 v1; v1 = Zero1() ; Variant2 v2; v2 = One2() ;

auto x = v1 * v2 ;

return x[0] == double(0) ; }

[snip] The attached contains a few minor corrections; however, there's still a few I don't know about. In particular, there's the shadowing. Maybe you have some idea how to correct some of the remaining problems. Compilation with gcc4.8 shows errors shown in 2nd attachment. -regards Larry