Move Semantics

Efficient Resource Transfers

Copying a large object copies all its data — expensive. Move semantics transfer ownership instead:

vector<int> makeData() {
    vector<int> v(1000000, 42);
    return v;  // moved out, not copied (NRVO / move)
}
auto data = makeData();  // no million-element copy!

std::move — explicitly move

string s1 = "Hello, World!";
string s2 = move(s1);   // s2 gets the data; s1 is now empty
cout << s2;              // Hello, World!
cout << s1.empty();      // true

Move constructor in your own class

class Buffer {
    int* data; int size;
public:
    Buffer(Buffer&& other)    // && means rvalue reference
        : data(other.data), size(other.size) {
        other.data = nullptr;  // leave other in valid state
        other.size = 0;
    }
};

Your Task

Write buildString(vector<string> words, string sep) that joins words with sep between them.