[모던C++입문] 6.4 서브 타입별 동적 선택

6.4 서브 타입별 동적 선택

• switch문을 이용해 프로그램을 동적으로 선택하도록 구현해보자.

class matrix {};
class vector {};

void cg(const matrix& A, const vector& b, vector& x);
void bicg(const matrix& A, const vector& b, vector& x);

struct solver
{
    virtual void operator()(const matrix& A, const vector& b, vector& x)= 0;
    virtual ~solver() {}
};

// 잠재적으로 템플릿화 됨
struct cg_solver : solver
{
    virtual void operator()(const matrix& A, const vector& b, vector& x) override 
    { cg(A, b, x); }    
};

struct bicg_solver : solver
{
    virtual void operator()(const matrix& A, const vector& b, vector& x) override 
    { bicg(A, b, x); }    
};


int main (int argc, char* argv[]) 
{
    using namespace std;
    matrix A;
    vector b, x;

    int solver_choice= argc >= 2 ? std::atoi(argv[1]) : 0;
    //일반적인 처리
    //복잡도에따라 확장하기 어렵다.
    switch (solver_choice) {
      case 0: cg(A, b, x); break;
      case 1: bicg(A, b, x); break;
    }

    // 팩토리 패턴 (C++11)
    unique_ptr<solver> my_solver;
    switch (solver_choice) {
      case 0: my_solver= unique_ptr<cg_solver>(new cg_solver); break;
      case 1: my_solver= unique_ptr<bicg_solver>(new bicg_solver); break;
    }

    // 팩토리 패턴 2
    //make_unique를 사용 (C++14)
    unique_ptr<solver> my_solver;
    switch (solver_choice) {
      case 0: my_solver= make_unique<cg_solver>(); break;
      case 1: my_solver= make_unique<bicg_solver>(); break;
    }

    (*my_solver)(A, b, x);
}