Summary - Move semantics

Combine std::move and move ctor to write a buffer class.

Summary - Move semantics

In this group you learned move semantics. T&& is an rvalue reference that binds to temporaries, and std::move converts an lvalue to an rvalue.

The move constructor T(T&&) transfers a resource to a new object, and move assignment T& operator=(T&&) transfers to an existing object. The rule of five says to define all five special members together. Now you will consolidate what you learned with two tasks: first an rvalue reference function, then moving with std::move.

Exercise Write an rvalue reference function

Define a function named show: its parameter is std::string&& s, its body is std::cout << s;. In main call show("Hello");.

Show example solution

#include <iostream>
#include <string>

void show(std::string&& s) {
    std::cout << s;
}

int main() {
    show("Hello");
    return 0;
}

Exercise Move a string with std::move

The starting code has a string a containing "World". Move the content of a into b with std::move and print b with std::cout.

Show example solution

#include <iostream>
#include <string>
#include <utility>

int main() {
    std::string a = "World";
    std::string b = std::move(a);
    std::cout << b;
    return 0;
}

End of section

You completed move semantics. You can now use the T&& rvalue reference and move with std::move.

With the move constructor and move assignment you transfer resources efficiently. The rule of five and rule of zero tell you when to write special members. The next group covers operator overloading; you will see the move assignment operator there in more detail.

Test yourself

What does std::move do?
```
std::string b = std::move(a);
```
- Deletes a
- Copies a
- Returns the address of a
- Converts a to an rvalue
Show answer

Converts a to an rvalue — std::move converts a to an rvalue.

rvalue reference parameter

void show(std::string____ s) { std::cout << s; }

Show answer

void show(std::string&& s) { std::cout << s; }

Next lesson: Operator functions

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