C++Now 2021

std::variant was added to C++ in 2017 as a type-safe alternative to C's union.
To start us off, I will shortly introduce the rationale of std::variant and the typical ways in which it can be used. I will also try to give insights into the way std::variant is typically implemented, highlighting the memory layout and its run-time performance implications.
The bulk of the talk will then focus on the key differences between std::variant and union, and discuss a common use-case where unions are typically used which std::variant does not support - serialization of streams of a trivially copyable object to files or to network. Then, I'll suggest approaches to tackle this shortcoming: Intrusive-Variant, Variant-of-Base. When presenting and describing the approaches above, I will dive deeper into what the C++ standard says about unions and their pitfalls, and discuss reasoning and issues. Time permitting, I'll finish off with a counterintuitive uses of std::variant - simple and safe mechanism for de-virtualization.
After attending this talk, participants should be better equipped to use this relatively new concept to modernize existing low-level C style code and will have a better understanding of how variants work under the hood.