C++ 함수 객체 (Fuction Object) 템플릿 / 람다식

장점 :

1. 다른 멤버 변수와 멤버 함수를 가질 수 있고 일반 함수에서 하지 못하는 지원을 받을 수 있습니다.
2. 함수 객체의 서명이 같더라도 객체 타입이 다르면 서로 전혀 다른 타입으로 인식합니다.
3. 일반 함수보다 빠릅니다. 
4. 인라인 될 수 있고(함수가 있어야 하므로 인라인 함수의 복사본 함수를 만들어 냄) 컴파일러가 쉽게 최적화 할 수 있습니다.

템플릿

enum class e_operation_type
{
    ADD,
    SUB,
    MUL,
    DIV,
    MAX
};
 
template<typename T>
class Template_function_obj
{
public:
    void operator()(e_operation_type _operation_type, T _lval, T _rval)
    {
        switch (_operation_type)
        {
        case e_operation_type::ADD: cout << "덧셈값 : " << to_string(_lval + _rval) << endl; break;
        case e_operation_type::SUB: cout << "뺄셈값 : " << to_string((_lval > _rval) ? (_lval - _rval) : (_rval - _lval)) << endl; break;
        case e_operation_type::MUL: cout << "곱셈값 : " << to_string(_lval * _rval) << endl; break;
        case e_operation_type::DIV: cout << "나눗셈값 : " << to_string((_lval > _rval) ? (_lval / _rval) : (_rval / _lval)) << endl; break;
 
        case e_operation_type::MAX: 
        default:
            break;
        }
    }
};
 
template<typename T = int>
void Test_msg(T& _val1, T& _val2)
{
    cout << "첫번째 숫자를 입력하세요. "; cin >> _val1;
    cout << "두번째 숫자를 입력하세요. "; cin >> _val2;
    cout << "테스트 중 / 값1 : " << _val1 << " 값2 : " << _val2 << endl;
}
 
int main()
{
    Template_function_obj<int>   int_function_obj;
    Template_function_obj<float> float_function_obj;
    int val1, val2;
 
    // int형 테스트
    Test_msg(val1, val2);
    int_function_obj(e_operation_type::ADD, val1, val2);
    int_function_obj(e_operation_type::SUB, val1, val2);
    int_function_obj(e_operation_type::MUL, val1, val2);
    int_function_obj(e_operation_type::DIV, val1, val2);
 
    // float형 테스트
    float float_val1, float_val2;
    cout << endl;
    Test_msg(float_val1, float_val2);
    float_function_obj(e_operation_type::ADD, float_val1, float_val2);
    float_function_obj(e_operation_type::SUB, float_val1, float_val2);
    float_function_obj(e_operation_type::MUL, float_val1, float_val2);
    float_function_obj(e_operation_type::DIV, float_val1, float_val2);
 
    return 0;
}

결과

람다식

class Function_obj
{
public:
    void operator()(std::function<void(int,int)> fn_ptr)
    {
        fn_ptr(5, 4);
    }
};
 
void Test_fn_obj()
{
    Function_obj function_obj;
    
    function_obj([](int a, int b)
        {
            cout << "덧셈값 : " << a + b << endl;
        });
 
    function_obj([](int a, int b)
        {
            cout << "뺄셈값 : " << a - b << endl;
        });
 
    function_obj([](int a, int b)
        {
            cout << "곱셈값 : " << a * b << endl;
        });
 
    function_obj([](int a, int b)
        {
            cout << "나눗셈값 : " << a / b << endl;
        });
}
 
int main()
{
    Test_fn_obj();
    return 0;
}

결과