Movement Algorithms

# Implementing a Custom Swap Function

## How can you implement a custom swap() function to optimize standard library algorithms?

Implementing a custom swap() function can optimize standard library algorithms such as std::ranges::reverse(), especially if your type has specific requirements or optimizations for swapping elements. Here's how you can doÂ it:

### Custom swap Function

First, define your custom type and implement the swapÂ function:

#include <algorithm>
#include <iostream>
#include <vector>

struct Player {
std::string name;
int score;

Player(std::string n, int s)
: name(n), score(s) {}

// Custom swap function
friend void swap(Player& a, Player& b) {
std::cout << "Swapping " << a.name
<< " with " << b.name << "\n";
std::swap(a.name, b.name);
std::swap(a.score, b.score);
}
};

int main() {
std::vector<Player> players{
{"Alice", 30}, {"Bob", 20}, {"Charlie", 40}
};

std::ranges::reverse(players);

for (const auto& player : players) {
std::cout << player.name << ": "
<< player.score << "\n";
}
}
Swapping Alice with Charlie
Charlie: 40
Bob: 20
Alice: 30

### How It Works

1. Define the Custom Type: We created a Player struct with a name and score.
2. Implement the swap() function: The swap() function swaps the name and score of two Player objects. Note the use of std::swap() within the custom swap().
3. Call the std::ranges::reverse() Algorithm: : When std::ranges::reverse() is called, it uses the custom swap() function to swap elements.

### Benefits

• Optimization: Custom swap logic can be more efficient than the default std::swap(), especially if the type has complex move semantics.
• Debugging: Adding print statements in the swap() function helps in debugging by showing when and how elements are swapped.

### Practical Example

Here's another example with a more complexÂ type:

#include <algorithm>
#include <iostream>
#include <vector>

struct ComplexType {
int data[100];

friend void swap(ComplexType& a, ComplexType& b) {
std::cout << "Swapping ComplexType objects\n";
for (int i = 0; i < 100; ++i) {
std::swap(a.data[i], b.data[i]);
}
}
};

int main() {
std::vector<ComplexType> vec(2);
std::ranges::reverse(vec);
}
Swapping ComplexType objects

### Conclusion

Implementing a custom swap() function allows you to tailor the swapping behavior to your specific type, which can optimize operations like std::ranges::reverse().

This is especially useful for types that have complex or costly move operations, ensuring efficient and correct elementÂ manipulation.

This Question is from the Lesson:

### Movement Algorithms

An introduction to the seven movement algorithms in the C++ standard library: move(), move_backward(), rotate(), reverse(), shuffle(), shift_left(), and shift_right().

Answers to questions are automatically generated and may not have been reviewed.

This Question is from the Lesson:

### Movement Algorithms

An introduction to the seven movement algorithms in the C++ standard library: move(), move_backward(), rotate(), reverse(), shuffle(), shift_left(), and shift_right().

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