class Shape_definition {
private:
	// ...
	std::vector<Instruction> items;			
public:
	//...
	friend std::istream& operator >> (std::istream& is, Shape_definition& def); // Объявлен дружественным
};
//-----------------------------------------------------------------------------
std::istream& operator >> (std::istream& is, Shape_definition& def);
//...

std::istream& operator >> (std::istream& is, Bushman::shp::Shape_definition& def){
	//...
	Bushman::shp::Instruction instr = Bushman::shp::Instruction::get_empty();
	while(is >> instr) def.items.push_back(instr); // Здесь проблема.
	return is;
}

std::istream& Bushman::shp::operator >> (std::istream& is, Bushman::shp::Shape_definition& def){//...}