What are the differences between std::optional and std::variant in C++17?

What are the differences between std::optional and std::variant in C++17?

std::optional is used to represent an optional value, while std::variant can hold one of several types. std::optional is ideal for cases where a value may or may not be present, whereas std::variant is useful when you need to work with multiple types.

Can you give an example of when to use std::optional?

Sure! Use std::optional when a function might not return a value. For instance, a function that searches for an item in a collection could return std::optional<Item> to indicate that the item may not be found.

And what about std::variant? When should I use that?

Use std::variant when you need a variable that can hold one of several different types. For example, if you have a function that can return either an integer or a string based on some condition, std::variant<int, std::string> would be appropriate.

Are there any performance considerations between the two?

Yes, std::optional typically has a smaller memory footprint than std::variant since it only needs to store one value. std::variant, on the other hand, requires enough space to store the largest type it can hold, which can lead to higher memory usage.