The addition of `std::variant` to the upcoming C++17 standard will introduce a "type-safe sum type" to the Standard Library. Variants model a "choice between types" - they essentially are type-safe "tagged unions".
The interface they expose, however, is often more cumbersome to use than it needs to be: defining exhaustive visitors requires the user to create a class with several
operator() overloads, or to create a chain of
if constexpr(...) calls. Both solutions are not very elegant.
After a brief overview of
std::variant and its usefulness, this talk will focus on the implementation of a "lambda-based in-place visitation" approach, where the user can visit a variant by simply providing a set of lambdas on the spot. This will require implementing a way of overloading arbitrary function objects.
Recursive variant types will then be covered and the "lambda-based" visitation techniques will be applied to them. This will require implementing the "Y combinator" higher-order function to achieve zero-runtime-overhead lambda recursion.
This talk is intended for developers familiar with C++11 and C++14 core language features (lambdas, variadic templates,
auto, etc...). Prior knowledge of
std::variant or sum types is not required.
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Implementing `variant` visitation using lambdas
Vittorio Romeo is a C++ enthusiast from a young age, now with a BS in Computer Science from the "Università degli Studi di Messina". While following the evolution of the C++ standard and embracing the newest features, he worked on several open-source projects, including modern general-purpose libraries and free cross-platform indie games. Vittorio is an active member of the C++ community, speaking at many conferences and events. He currently maintains a YouTube channel featuring well-received modern C++11 and C++14 tutorials. When he's not writing code, Vittorio enjoys weightlifting and fitness-related activities, competitive/challenging computer gaming and good sci-fi movies/TV-series.