Runtime polymorphism usually connects with v-tables and virtual functions. However, in this blog post, I’ll show you a modern C++ technique that leverages std::variant and std::visit. This C++17 technique might offer not only better performance and value semantics but also interesting design patterns.
Last Update: 2nd Nov 2020 (Passing arguments, Build time benchmark, fixes).
Continuing the topic from last week, let’s dive into the topic of std::invoke. This helper template function helps with uniform syntax call for various callable object types and can greately reduce the complexity of our generic code.
Ranges and Projections In C++20 there are handful of rangified algorithms. As a simple example let’s say we want to sort a vector of integers:
When you see an article about new C++ features, most of the time you’ll have a description of major elements. Looking at C++17, there are a lot of posts (including articles from this blog) about structured bindings, filesystem, parallel algorithms, if constexpr, std::optional, std::variant… and other prominent C++17 additions.
With the addition of Ranges and Concepts in C++20, our good old algorithm interfaces got super long “rangified” versions. For example, copy is now 4 lines long… and it’s just the declaration!
template <ranges::input_range R, std::weakly_incrementable O> requires std::indirectly_copyable<ranges::iterator_t<R>, O> constexpr ranges::copy_result<ranges::borrowed_iterator_t<R>, O> copy(R&& r, O result); How to decipher such a long declaration?
C++ grows very fast! For example, the number of pages of the C++ standard went from 879 pages for C++98⁄03 to 1834 for C++20! Nearly 1000 pages! What’s more, with each revision of C++, we get several dozens of new features. Have a look at my blog post with all C++17 features, it shows 48 items, and my C++20 reference card lists 47 elements!
Variadic templates and argument packs which are available since C++11 give flexibility in situations when you don’t know the number of inputs upfront. However, they are limited and can only appear at the end of the type sequence.
Have a look at today’s blog post from Jonathan Boccara, who describes a technique that might improve this situation.
Since a few months, I’ve been refactoring my old C++/OpenGL project. Thus far, I used compilers (MSVC and Clang), my knowledge or free tools. At some point, I also got a chance to leverage a solid static analysis tool - PVS-Studio. The tool helped me with identifying 8 critical issues not to mention good code style and performance enhancements (in total 137 warnings)
Some time ago I wrote about a new way to implement runtime polymorphism which is based not on virtual functions but on std::visit and std::variant. Please have a look at this new blog post where I experiment with this approach on my home project. The experiment is more practical than artificial examples.
I took my old pet project from 2006, experimented, refactored it and made it more modern C++. Here are my lessons and six practical steps that you can apply in your projects.
Background And Test Project All changes that I describe here are based on my experience with a pet project which I dig out from the studies.
In my previous article on polymorphic allocators, we discussed some basic ideas. For example, you’ve seen a pmr::vector that holds pmr::string using a monotonic resource. How about using a custom type in such a container? How to enable it? Let’s see.
The Goal In the previous article there was similar code:
Up to (and including) C++17 if you wanted to check the start or the end in a string you have to use custom solutions, boost or other third-party libraries. Fortunately, this changes with C++20.
See the article where I’ll show you the new functionalities and discuss a couple of examples.
We’re on the last day of the lambda week. We have all the essential knowledge, and now we can learn some tricks!
The Series This blog post is a part of the series on lambdas:
The syntax changes (Tuesday 4th August) Capturing things (Wednesday 5th August) Going generic (Thursday 6th August) Tricks (Friday 5th August)(this post) +() Have a closer look: