The Strategy Design Pattern a Behavioral Pattern using C++

The Strategy Design Pattern is a behavioral design pattern that enables selecting an algorithm's implementation at runtime. Instead of implementing a single algorithm directly, a class can be designed to use multiple algorithms interchangeably. The Strategy pattern encapsulates each algorithm inside a separate class, known as a strategy class, allowing them to be switched in and out as required. This design aids in decoupling the algorithm's definition from its usage.
Why C++ Programmers Should Study It

• Flexibility Allows dynamic swapping of algorithms based on runtime conditions.
• Encapsulation Encapsulates algorithm variations, making them interchangeable.
• Maintainability Simplifies maintenance by decoupling algorithm implementation from its context.
• Scalability Eases addition of new strategies without altering the context.
• Reusability Facilitates algorithm reuse across different contexts or applications.
• Testability Enhances testability by isolating the context from the strategy.
• Design Cleanliness Promotes cleaner design by separating concerns and reducing conditional statements.

The Strategy design pattern implemented in C++. We'll create three classes: Strategy, ConcreteStrategyA, and ConcreteStrategyB. The Strategy class is an interface defining a family of algorithms, while `ConcreteStrategyA` and `ConcreteStrategyB` are concrete implementations of these algorithms. We'll also create a Context class which maintains a reference to a `Strategy` object and allows the client to switch between different strategies dynamically. Let's start with the header files: Strategy.h

// Abstract Strategy class
class Strategy {
public:
    virtual ~Strategy() {}
    virtual void execute() = 0;
};

ConcreteStrategyA.h

#include "Strategy.h"

// Concrete Strategy A class
class ConcreteStrategyA : public Strategy {
public:
    void execute() override;
};

ConcreteStrategyB.h

#include "Strategy.h"

// Concrete Strategy B class
class ConcreteStrategyB : public Strategy {
public:
    void execute() override;
};

Context.h

#include "Strategy.h"

// Context class
class Context {
public:
    Context(Strategy* strategy);
    void setStrategy(Strategy* strategy);
    void executeStrategy();

private:
    Strategy* strategy_;
};

Now let's implement these classes: ConcreteStrategyA.cpp

#include <iostream>
#include "ConcreteStrategyA.h"

void ConcreteStrategyA::execute() {
    std::cout << "Executing Concrete Strategy A\n";
    // Implementation of strategy A
}

ConcreteStrategyB.cpp</b>

#include <iostream>
#include "ConcreteStrategyB.h"

void ConcreteStrategyB::execute() {
    std::cout << "Executing Concrete Strategy B\n";
    // Implementation of strategy B
}

Context.cpp

#include "Context.h"

Context::Context(Strategy* strategy) : strategy_(strategy) {}

void Context::setStrategy(Strategy* strategy) {
    strategy_ = strategy;
}

void Context::executeStrategy() {
    if (strategy_)
        strategy_->execute();
}

And finally,the main.cpp file:
main.cpp

#include <iostream>
#include "ConcreteStrategyA.h"
#include "ConcreteStrategyB.h"
#include "Context.h"

int main() {
    ConcreteStrategyA strategyA;
    ConcreteStrategyB strategyB;
    
    Context context(&strategyA); // Start with strategy A
    context.executeStrategy(); // Output should be "Executing Concrete Strategy A"
    
    context.setStrategy(&strategyB); // Switch to strategy B
    context.executeStrategy(); // Output should be "Executing Concrete Strategy B"
    
    return 0;
}

The order to create the classes in your project would be:

1. Strategy
2. ConcreteStrategyA
3. ConcreteStrategyB
4. Context

When you run the code, you should see the output:

Executing Concrete Strategy A
Executing Concrete Strategy B>

This demonstrates the Strategy design pattern, where the behavior of the `Context` object can be changed dynamically by switching between different `Strategy` objects.