What are some examples of using std::variant in C++17?

Can you give me some examples of using std::variant in C++17?

Sure! std::variant is a type-safe union that can hold one of several types. Here's a simple example:

#include <variant>
#include <iostream>

std::variant<int, float, std::string> myVariant;

myVariant = 42; // holds an int
std::cout << std::get<int>(myVariant) << std::endl;

myVariant = 3.14f; // now holds a float
std::cout << std::get<float>(myVariant) << std::endl;

myVariant = "Hello, World!"; // now holds a string
std::cout << std::get<std::string>(myVariant) << std::endl;

This code demonstrates how to assign different types to a std::variant and retrieve them.

What happens if I try to get a type that isn't currently held?

If you try to get a type that isn't currently held by the std::variant, it will throw a std::bad_variant_access exception. You can also use std::get_if to safely check the type before accessing it.

Can you show me how to use std::get_if?

Absolutely! Here's how you can use std::get_if:

if (auto pVal = std::get_if<int>(&myVariant)) {
    std::cout << "It's an int: " << *pVal << std::endl;
} else {
    std::cout << "It's not an int." << std::endl;
}

This checks if myVariant holds an int and safely retrieves it if it does.

Are there any limitations to using std::variant?

Yes, std::variant has some limitations. For instance, all types must be copyable and assignable. Also, it can only hold one value at a time, so you need to manage the state carefully.