Structural_patterns

Structural Patterns

Structural patterns describe how objects are composed to form larger structures.

Adapter

Convert one interface to another:

class OldAPI {
public:
    int process(int data) { return data * 2; }
};

class NewAPI {
public:
    virtual int processData(std::string) = 0;
};

class Adapter : public NewAPI {
    OldAPI old;
public:
    int processData(std::string data) override {
        return old.process(std::stoi(data));
    }
};

Decorator

Add behavior dynamically:

class Coffee {
public:
    virtual double cost() = 0;
};

class BasicCoffee : public Coffee {
public:
    double cost() override { return 5.0; }
};

class MilkDecorator : public Coffee {
    Coffee* coffee;
public:
    MilkDecorator(Coffee* c) : coffee(c) {}
    double cost() override { return coffee->cost() + 1.5; }
};

Facade

Simplified interface to complex system:

class CPU { void freeze() {} }
class Memory { void load() {} }
class HardDrive { void read() {} }

class ComputerFacade {
    CPU cpu;
    Memory memory;
    HardDrive hd;
public:
    void start() {
        cpu.freeze();
        memory.load();
        hd.read();
    }
};

Proxy

Placeholder for another object:

class RealImage {
public:
    void display() { /* Load high-res */ }
};

class ImageProxy {
    RealImage* realImage;
public:
    void display() {
        if (!realImage) {
            realImage = new RealImage();
        }
        realImage->display();
    }
};