2 Lines Of Code and 3 C++17 Features - The overload Pattern

by Bartlomiej Filipek

While I was doing research for my book and blog posts about C++17 several times I stumbled upon this pattern for visitation of std::variant:

template<class... Ts> struct overload : Ts... { using Ts::operator()...; };
template<class... Ts> overload(Ts...) -> overload<Ts...>;

With the above pattern, you can provide separate lambdas “in-place” for visitation.

It’s just two lines of compact C++ code, but it packs a few interesting concepts.

Let’s see how this thing works and go through the three new C++17 features that make this patter possible...

C++20: Concepts - Predefined Concepts

by Rainer Grimm

C++20 has many predefined concepts. Consequentially, before you define your concept, you should know the existing ones. This post gives you an overview of the predefined concepts. To get the general idea of concepts, read my previous posts...

Objects, their lifetimes and pointers

by Dawid Pilarski

A detailed tour on C++ objects, what they are and how to avoid common undefined behaviors.

Dry-comparisons: A C++ Library to Shorten Redundant If Statements

by Jonathan Boccara

Have you ever felt that the code you write in if statements doesn’t look as natural as the specification expresses them?

C++ coroutines: The problem of the DispatcherQueue task that runs too soon, part 4

by Raymond Chen

Last time, we made another attempt to fix a race condition in C++/WinRT’s resume_foreground(Dispatcher­Queue) function when it tries to resume execution on a dispatcher queue. We did this by having the queued task wait until await_suspend was finished before allowing the coroutine to resume, and we found a nice place to put the synchronization object, namely in the awaiter, but even with that fix, we introduced additional memory barriers into the hot code path.

But it turns out all this work was unnecessary. We just had to look at the problem a different way.

The purpose of storing the result of Try­Enqueue into m_queued is so that await_resume can report whether the lambda was queued or not. But we can infer that information another way: The fact that our lambda is running means that got got queued. Because if the lambda were not queued, then it would never have run in the first place...

C++ coroutines: The problem of the DispatcherQueue task that runs too soon, part 3

by Raymond Chen

Last time, we fixed a race condition in C++/WinRT’s resume_foreground(Dispatcher­Queue) function when it tries to resume execution on a dispatcher queue. We did this by having the queued task wait until await_suspend was finished before allowing the coroutine to resume. The hard part was finding a place to put the synchronization object, and we ended up putting it in the queued task’s lambda...

Launching the Meeting C++ Community Survey

by Jens Weller

One thing then often has bugged me when looking at the C++ community is that we don't really had good numbers on most things. Jetbrains, ISOCPP and Bartek's coding blog have launched surveys in the last years, which changed this a little. Also I've been doing some surveys on Twitter, giving some limited insight into C++ related topics. But Twitter surveys are very limited, and for a long time I had an idea on how to make this a continuous survey.

C++ User Group meetings in January 2020

by Jens Weller

Happy new years! The year has begun, and lots of C++ User Groups have their first meeting of 2020.

Would like to start your own group or looking for ideas in running your current group? Watch my talk from CppCon:

CppCon YT - CppCon 2019: Jens Weller “Starting and Running C++ User Groups”

C++ coroutines: The problem of the DispatcherQueue task that runs too soon, part 2

by Raymond Chen

Last time, we discovered a race condition in C++/WinRT’s resume_foreground(Dispatcher­Queue) function when it tries to resume execution on a dispatcher queue. Let’s try to fix it...

C++ coroutines: The problem of the synchronous apartment-changing callback

by Raymond Chen

Today is a puzzle you can you can try to solve with the information you’ve learned about C++ coroutines and C++/WinRT...