Using std::optional for class members

std::optional is a great choice for class members that may or may not have a value. Here's an example of how you can use it:

1#include <optional>
2#include <string>
3
4class Player {
5public:
6  Player(const std::string& name) : name(name){}
7
8  void set_level(int level) {
9    this->level = level;
10  }
11
12  std::optional<int> get_level() const {
13    return level;
14  }
15
16private:
17  std::string name;
18  std::optional<int> level;
19};

In this example, the Player class has a name member which is always present, and a level member which is optional. The level member is not initialized in the constructor, so it starts off empty.

The set_level function sets the level member to a specific value, making it non-empty.

The get_level function returns the level member. If level has been set, it will return an std::optional containing the level value. If level has not been set, it will return an empty std::optional.

Here's how you might use this class:

1#include <optional>
2#include <string>
3#include <iostream>
4
Player Class|Show
5class Player {/*...*/}
22
23int main() {
24  Player player("Hero");
25
26  if (player.get_level()) {
27    std::cout << "Player level: "
28      << *player.get_level() << std::endl;
29  } else {
30    std::cout << "Player level not set"
31      << std::endl;
32  }
33
34  player.set_level(5);
35
36  if (player.get_level()) {
37    std::cout << "Player level: "
38      << *player.get_level() << std::endl;
39  } else {
40    std::cout << "Player level not set";
41  }
42}

This will output:

1Player level not set
2Player level: 5

Using std::optional for class members is a safe and expressive way to handle values that may not be present. It clearly separates the "value not set" state from any possible value the member could have, including default-constructed values.