C++20

C++20 will be the next big C++ standard after C++11. As C++11 did it, C++20 will change the way we program modern C++. This change is, in particular, true for Ranges, Coroutines, Concepts, and Modules. To understand this next big step in the evolution of C++, let me put it in this post in the historical context of C++ standards.

I wrote a few posts about using concepts. Concepts are a named set of requirements. Let's define a few concepts in this post.

The unification of templates, concepts, and placeholders goes on. This time, I will have a closer look at constrained (concepts) and unconstrained (auto) placeholders in the context of templates.

C++11 has auto unconstrained placeholders. You can use concepts in C++20 as constrained placeholders. What seems at first glimpse not so thrilling is for me the decisive quantum leap. C++ templates will become an easy to use C++ feature.

Task blocks use the well-known fork-join paradigm for the parallel execution of tasks.

Transactional memory is based on the idea of a transaction from the database theory. Transactional memory shall make the handling of threads a lot easier. That for two reasons. Data races and deadlocks disappear. Transactions are composable.

Coroutines are functions that can suspend and resume their execution while keeping their state. The evolution in C++20 goes one step further.

Latches and barriers are simple to thread synchronisation mechanism which enables it that some threads wait until a counter becomes zero. We will presumably in C++20 get latches and barriers in three variations: std::latch, std::barrier, and std::flex_barrier.

Tasks in the form of promises and futures have in C++11 an ambivalent reputation. On the one hand, they are a lot easier to use than threads or condition variables; on the other hand, they have a great deficiency. They can not be composed. C++20 will overcome this deficiency.

C++20 will have atomic smart pointers. To be exactly, we will get a std::atomic_shared_ptr and a std::atomic_weak_ptr. But why? std::shared_ptr and std::weak_ptr are already thread-safe. Sort of. Let me dive into the details.