Constrained Dynamic Types using Unions and std::variant

Learn how to store dynamic data types in C++ using unions and the type-safe std::variant

Ryan McCombe
Updated
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Questions & Answers

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When should I use std::variant instead of a union?
What are the advantages of using std::variant over a regular union in C++? When is it better to use std::variant?
How can I default construct a variant with non-default-constructible types?
If I have a std::variant with types that are not default-constructible, how can I still default construct the variant?
What is the difference between std::variant and std::any?
How does std::variant differ from std::any in C++? When would I use one over the other?
How do I handle errors when using std::variant?
What are the best practices for error handling when using std::variant in C++? How do I deal with exceptions and invalid accesses?
What are the performance characteristics of std::variant?
How does std::variant perform compared to other ways of storing multiple types, like unions or inheritance? Are there any performance pitfalls to watch out for?
How can I define a recursive variant type?
Is it possible to have a variant that contains a type that itself contains the same variant type? How would I define such a recursive variant?
What is the difference between std::variant and std::optional?
How does std::variant differ from std::optional in C++? When would I choose to use one over the other?