Strategy design pattern in C++; When and how to use it

The Strategy design pattern is a behavioral design pattern that defines a family of algorithms, encapsulates each one, and makes them interchangeable. This pattern allows you to choose the appropriate algorithm at runtime, providing flexibility and extensibility to your code. Here's how to use the Strategy pattern in C++ and when to use it:

When to Use the Strategy Design Pattern:

1. Multiple Algorithms: Use the Strategy pattern when you have multiple algorithms that can be used interchangeably for a specific task. For example, sorting algorithms like quicksort, mergesort, or bubblesort.

2. Runtime Algorithm Selection: When you need to select an algorithm at runtime, the Strategy pattern is beneficial. It allows you to choose the algorithm based on user input, configuration, or other runtime conditions.

3. Avoid Conditional Statements: If you want to avoid using long chains of conditional statements (if-else or switch-case) to select different behaviors, the Strategy pattern helps simplify the code by encapsulating these behaviors in separate classes.

How to Implement the Strategy Design Pattern in C++:

Here's a step-by-step guide on how to implement the Strategy pattern in C++:

Step 1: Define the Strategy Interface

Create an abstract class or interface (in C++, you typically use an abstract class) that defines the interface for all concrete strategies. This class will have a method that represents the algorithm to be executed.

cppCopy codeclass SortingStrategy {
public:
    virtual void sort(std::vector<int>& data) = 0;
    virtual ~SortingStrategy() {}
};

Step 2: Create Concrete Strategy Classes

Implement concrete strategy classes that inherit from the strategy interface. Each concrete strategy class should provide its own implementation of the algorithm.

cppCopy codeclass QuickSort : public SortingStrategy {
public:
    void sort(std::vector<int>& data) override {
        // Implement quicksort algorithm here
    }
};

class MergeSort : public SortingStrategy {
public:
    void sort(std::vector<int>& data) override {
        // Implement mergesort algorithm here
    }
};

Step 3: Context Class

Create a context class that contains a reference to the strategy interface. This class will allow you to switch between different strategies dynamically.

cppCopy codeclass SortContext {
private:
    SortingStrategy* strategy;

public:
    SortContext(SortingStrategy* strategy) : strategy(strategy) {}

    void setStrategy(SortingStrategy* newStrategy) {
        strategy = newStrategy;
    }

    void performSort(std::vector<int>& data) {
        strategy->sort(data);
    }
};

Step 4: Client Code

In your client code, create instances of the concrete strategy classes and use the context class to perform sorting. You can switch between strategies at runtime.

cppCopy codeint main() {
    std::vector<int> data = {5, 2, 9, 1, 5, 6};

    SortContext context(new QuickSort());
    context.performSort(data);

    // Switch to a different sorting strategy at runtime
    context.setStrategy(new MergeSort());
    context.performSort(data);

    return 0;
}

By using the Strategy design pattern in C++, you can easily switch between different sorting algorithms without modifying the client code extensively. This pattern promotes code reusability, maintainability, and flexibility in choosing algorithms at runtime, making it a valuable tool in software design.