Method at

inst/include/Rcpp/vector/Matrix.h:144–146

    }

    inline Proxy at( const size_t& i, const size_t& j) {
        return static_cast< Vector<RTYPE>* >( this )->operator()( i, j ) ;
    }
    inline const_Proxy at( const size_t& i, const size_t& j) const {
        return static_cast< const Vector<RTYPE>* >( this )->operator()( i, j ) ;
    }