考虑以下代码:
template <typename T>
class DrawerFactory
{
protected:
DrawerFactory() {};
private:
virtual shared_ptr<IDrawer> GetDrawer(T settings) = 0;
};
class ConcreteDrawerFactoryA : public DrawerFactory<SettingsA>
{
public:
shared_ptr<IDrawer> GetDrawer(SettingsA settingsA) override
{
if (settingsA.style == A) return make_shared<ConcreteDrawerA>(settingsA.length, settingsA.stroke, settingsA.opacity);
else return make_shared<ConcreteDrawerB>(20, .5);
};
};
class ConcreteDrawerFactoryB : public DrawerFactory<SettingsB>
{
public:
shared_ptr<IDrawer> GetDrawer(SettingsB settingsB) override
{
if (settingsB.type == TYPEC) return make_shared<ConcreteDrawerC>(settingsB.width, settingsB.height);
else return make_shared<ConcreteDrawerD>(10, 2);
};
};
我可以通过以下方式获得一个抽屉:
ConcreteDrawerFactoryA().GetDrawer(settingsa);
或
ConcreteDrawerFactoryB().GetDrawer(settingsb);
我想做的是:
DrawerFactory().GetDrawer(settingsa);
DrawerFactory().GetDrawer(settingsb);
有没有一种方法可以设置它,而不必为我想添加的每个具体工厂不断地向 DrawerFactory
添加重载?
最佳答案
您可以使用模板和特化来代替工厂层次结构和虚拟分派(dispatch):
#include <memory>
struct IDrawer { };
struct Drawer1: IDrawer { };
struct Drawer2: IDrawer { };
struct Drawer3: IDrawer { };
struct Drawer4: IDrawer { };
template <class T>
struct DrawerGetterImpl;
struct DrawerFactory {
template <class T>
std::shared_ptr<IDrawer> GetDrawer(T settings) {
return DrawerGetterImpl<T>::GetDrawer(settings);
}
};
struct SettingsA { int style; };
template <>
struct DrawerGetterImpl<SettingsA> {
static std::shared_ptr<IDrawer> GetDrawer(SettingsA settings) {
if (settings.style == 1) {
return std::make_shared<Drawer1>();
}
return std::make_shared<Drawer2>();
}
};
struct SettingsB { int type; };
template <>
struct DrawerGetterImpl<SettingsB> {
static std::shared_ptr<IDrawer> GetDrawer(SettingsB settings) {
if (settings.type == 1) {
return std::make_shared<Drawer3>();
}
return std::make_shared<Drawer4>();
}
};
int main() {
DrawerFactory().GetDrawer(SettingsA{1});
}
关于c++ - 多态工厂,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/41286072/