C++ copy and move example

main.cpp

#include <iostream>
#include <vector>
#include <utility>

using namespace std;

// Reference
// https://learn.microsoft.com/ko-kr/cpp/cpp/move-constructors-and-move-assignment-operators-cpp?view=msvc-170
class Block {
public:
    Block(size_t length=0): buffer(vector<int>(length)) {
        cout << "Block initialized (length=" << length << ")" << endl;
    }
    Block(const Block& block): buffer(block.buffer) {
        cout << "Block copied (length=" << buffer.size() << ")" << endl;
    }
    Block(Block&& block) {
        *this = move(block);
        cout << "Block moved (length=" << buffer.size() << ")" << endl;
    }
    ~Block() {
        cout << "Block deleted (length=" << buffer.size() << ")" << endl;
    }
    
    Block& operator=(const Block& block) {
        buffer = block.buffer;
        return *this;
    }
    Block& operator=(Block&& block) {
        buffer = move(block.buffer);
        return *this;
    }
    
    // Reference
    // https://stackoverflow.com/questions/10360232/how-do-i-use-a-chain-of-operator-overloads-without-modifying-the-operands
    Block& operator+=(const Block& block) {
        buffer.insert(
            buffer.end(), 
            block.buffer.begin(),
            block.buffer.end()
        );
        return *this;
    }
    
public:
    vector<int> buffer;
};

Block operator+(Block a, const Block& b) {
    // Note that "return a+=b;" invokes the copy constructor, not the move constructor.
    // The type of "a+=b" is Block& but the return type is Block.
    a += b;
    return a;
}

int main () {
    cout << "copy" << endl;
    {
        Block block(10);
        // Block initialized (length=10)
        
        Block copied = block;
        // Block copied (length=10)
        
        // Block deleted (length=10)
        // Block deleted (length=10)
    }
    cout << endl;
    
    cout << "move" << endl;
    {
        Block block(20);
        // Block initialized (length=20)
        
        Block moved = move(block);
        // Block moved (length=20)
        
        // Block deleted (length=20)
        // Block deleted (length=0)
    }
    cout << endl;
    
    cout << "operator+ with constructors(rvalue)" << endl;
    {
        Block sum = Block(10) + Block(20) + Block(30) + Block(40);
        // Block initialized (length=40)
        // Block initialized (length=30)
        // Block initialized (length=20)
        // Block initialized (length=10)
        // Block moved (length=30)
        // Block moved (length=60)
        // Block moved (length=100)
        // Block deleted (length=0)
        // Block deleted (length=0)
        // Block deleted (length=0)
        // Block deleted (length=20)
        // Block deleted (length=30)
        // Block deleted (length=40)
        
        cout << "sum.buffer.size() = " << sum.buffer.size() << endl;
        // sum.buffer.size() = 100
        
        // Block deleted (length=100)
    }
    cout << endl;
    
    cout << "operator+ with variables(lvalue)" << endl;
    {
        Block a(10), b(20), c(30), d(40);
        // Block initialized (length=10)
        // Block initialized (length=20)
        // Block initialized (length=30)
        // Block initialized (length=40)
        
        Block sum = a + b + c + d;
        // Block copied (length=10)
        // Block moved (length=30)
        // Block moved (length=60)
        // Block moved (length=100)
        // Block deleted (length=0)
        // Block deleted (length=0)
        // Block deleted (length=0)
        
        cout << "sum.buffer.size() = " << sum.buffer.size() << endl;
        // sum.buffer.size() = 100
        
        // Block deleted (length=100)
        // Block deleted (length=40)
        // Block deleted (length=30)
        // Block deleted (length=20)
        // Block deleted (length=10)
    }
    cout << endl;
    
    return EXIT_SUCCESS;
}