Abstract Factory Pattern
Published:
虛擬工廠? 那我們要生產什麼?? 其實這就是 parent class 中 virtual function 的感覺
- 相比於 factory pattern 透過單一介面管理每個類的生產
- 虛擬工廠 更像是定義好了這個工廠具有什麼功能
此為風格工廠 (抽象)
- art deco 裝飾藝術風格
- victorian 維多利亞風格
- modern 現代風格
Scenario
什麼時候適合用 Abstract Factory Pattern?
當今天有很多不同的角色，都需要做同樣類型的事情，那就很適合用 Abstract Factory Pattern
黑悟空
- 滑鼠左鍵: 金箍棒變長往前打
- 上鍵: 三隻腳走路 (搭配額外一根)
但悟空會72變… 今天多了一變 (變形金剛)
- 滑鼠左鍵:
- 黑悟空: 金箍棒變長往前打
- 金剛: 手臂變成砲管 發射飛彈
- 上鍵:
- 黑悟空: 三隻腳走路 (搭配額外一根)
- 金剛: 腳噴氣 起飛
Case Study
Without Pattern
void user_press_left_bottom(std::string character) {
if (character == "Wukong") {
std::cout << "Wukong attack" << std::endl;
} else (character == "Optimus") {
std::cout << "Optimus Prime attack" << std::endl;
}
}
void user_press_up() {
if (character == "Wukong") {
std::cout << "Wukong jump" << std::endl;
} else (character == "Optimus") {
std::cout << "Optimus Prime fly" << std::endl;
}
}
With Abstract Factory Pattern
class Character {
public:
virtual void attack() = 0;
virtual void move() = 0;
};
class Wukong : public Character {
public:
void attack() override {std::cout << "Wukong attack" << std::endl;}
void move() override {std::cout << "Wukong jump" << std::endl;}
};
class Transformer : public Character {
public:
void attack() override {std::cout << "Optimus Prime attack" << std::endl;}
void move() override {std::cout << "Optimus Prime fly" << std::endl;}
};
void user_press_left_bottom(Character* character) {
character->attack();
}
void user_press_up(Character* character) {
character->move();
}
Pros & Cons
Pros
- You can be sure that the products you’re getting from a factory are compatible with each other.
- You avoid tight coupling between concrete products and client code.
- Single Responsibility Principle. You can extract the product creation code into one place, making the code easier to support.
- Open/Closed Principle. You can introduce new variants of products without breaking existing client code.
Cons
The code may become more complicated than it should be, since a lot of new interfaces and classes are introduced along with the pattern.