What’s the point of std::monostate? You can’t do anything with it! -- Raymond Chen

By Blog Staff | Jul 29, 2024 11:35 AM | Tags: None

C++17 introduced std::monostate, a dummy type with no members and trivial functions, primarily used when no action is needed. Despite its simplicity, std::monostate plays a crucial role in scenarios like coroutines and std::variant, where a default-constructible placeholder type is required.

What’s the point of std::monostate? You can’t do anything with it!

by Raymond Chen

From the article:

C++17 introduced std::monostate, and I used it as a placeholder to represent the results of a coroutine that produces nothing. In the comments, Neil Rashbrook asked what you are expected to do with a std::monostate, seeing as has no members and only trivial member functions.

The answer is “nothing”.

The purpose of std::monostate is to be a dummy type that does nothing. All instances are considered equal to each other. It is basically this:

struct monostate {};
// plus relational operators and a hash specialization

You can see it in libcxx (LLVM/clang), libstdc++ (gcc), and stl (msvc).

CppCon 2024 Creating a Sender/Receiver HTTP Server -- Dietmar Kühl

By Blog Staff | Jul 29, 2024 08:27 AM | Tags: None

Registration is now open for CppCon 2024! The conference starts on September 15 and will be held in person in Aurora, CO. To whet your appetite for this year’s conference, we’re posting some upcoming talks that you will be able to attend this year. Here’s another CppCon future talk we hope you will enjoy – and register today for CppCon 2024!

Creating a Sender/Receiver HTTP Server 

Monday, September 16 • 11:00 - 12:00 MDT

by Dietmar Kühl

Summary of the talk:

The sender/receiver framework for asynchronous operations in C++ is well on its way towards standardization in C++26. Previously, the theoretical background and implementation of the framework was shown but there wasn't much detail on how an application using sender/receiver would look like.

This presentation shows how to create a simple HTTP server using the sender/receiver framework with matching networking senders together with a coroutine task and and async scope. The code is created live using fundamental facilities. The goal is to demonstrate that the use of an asynchronous framework doesn't necessarily lead to excessive complexity when using C++'s facilities effectively. The resulting server could be embedded into any application, e.g., to inspect its state or change configurations. The takeaway is that it is reasonably straight forward to create an asynchronous program.

Dietmar Kühl is a senior software developer at Bloomberg L.P. working on the data distrubtion environment used both internally and by enterprise installations at clients. In the past, he has done mainly consulting for software projects in the finance area. He is a regular attendee of the ANSI/ISO C++ standards committee, frequent presenter at the ACCU conference, and a moderator of the newsgroup comp.lang.c++.moderated.

CppCon 2023 Undefined Behavior in C++: What Every Programmer Should Know and Fear -- Fedor Pikus

By Blog Staff | Jul 26, 2024 05:06 AM | Tags: None

Registration is now open for CppCon 2024! The conference starts on September 15 and will be held in person in Aurora, CO. To whet your appetite for this year’s conference, we’re posting videos of some of the top-rated talks from last year's conference. Here’s another CppCon talk video we hope you will enjoy – and why not register today for CppCon 2024!

Undefined Behavior in C++: What Every Programmer Should Know and Fear

by Fedor Pikus

Summary of the talk:

This talk is about You-Know-What, the thing in our programs we don’t mention by name.

What is this undefined behavior every C++ programmer has grown to fear? Just as importantly, what it isn’t? If it’s so scary, why is it allowed to exist in the language?
The aim of this talk is to approach undefined behavior rationally: without fear but with due caution. We will learn why the standard allows undefined behavior in the first place, what actually happens when a program does something the standard calls “undefined,” and why it must be taken seriously even when the program “works as-is.” As this is a practical talk, we will have live demos of programs with undefined behavior and sometimes unexpected outcomes (if you are very lucky, you might see demons fly out of the speaker’s nose). Also, as this is a practical talk, we will learn how to detect undefined behavior in one’s programs, and how to take advantage of the undefined behavior to gain better performance.

Concurrency: From Theory to Practice -- Lucian Radu Teodorescu

By Blog Staff | Jul 22, 2024 03:32 PM | Tags: None

Concurrency is a complicated topic. Lucian Radu Teodorescu provides a simple theory of concurrency which is easy to reason about and apply.

Concurrency: From Theory to Practice

by Lucian Radu Teodorescu

From the article:

One of the big challenges with concurrency is the misalignment between theory and practice. This includes the goals of concurrency (e.g., improving the performance of the application) and the means we use to achieve that goal (e.g., blocking primitives that slow down the program). The theory of concurrency is simple and elegant. In practice, concurrency is often messy and strays from the good practices of enabling local reasoning and using structured programming.

We present a concurrency model that starts from the theory of concurrency, enables local reasoning, and adheres to the ideas of structured programming. We show that the model can be put into practice and that it yields good results.

Most of the ideas presented here are implemented in a C++ library called concore2full [concore2full]. The library is still a work in progress. The original goal for this model and for this library was its inclusion in the Hylo programming language [Hylo]. For Hylo, we want a concurrency model that allows local reasoning and adheres to the structured programming paradigm. We also wanted a model in which there is no function colouring [Nystrom15], in which concurrency doesn’t require a different programming paradigm.

This article is based on a talk I gave at the ACCU 2024 conference [Teodorescu24]. The conference was great! The programme selection was great; there was always something of interest to me. With many passionate C++ engineers and speakers, the exchange of information between participants was excellent; as they say, the best track was the hallway track. I highly encourage all C++ enthusiasts (and not just C++) to participate in future ACCU conferences.

CppCon 2023 Thread Safety With synchronized_value in C++ -- Jørgen Fogh

By Blog Staff | Jul 20, 2024 01:12 PM | Tags: None

Registration is now open for CppCon 2024! The conference starts on September 15 and will be held in person in Aurora, CO. To whet your appetite for this year’s conference, we’re posting videos of some of the top-rated talks from last year's conference. Here’s another CppCon talk video we hope you will enjoy – and why not register today for CppCon 2024!

Lightning Talk: Thread Safety With synchronized_value in C++

by Jørgen Fogh

Summary of the talk:

Adding thread safety to existing code is hard. The proposed type synchronized_value makes it less hard.
I will show you why.

CppCon 2023 The Responsibility of C++ -- Neil Henderson

By Blog Staff | Jul 18, 2024 05:01 AM | Tags: None

Registration is now open for CppCon 2024! The conference starts on September 15 and will be held in person in Aurora, CO. To whet your appetite for this year’s conference, we’re posting videos of some of the top-rated talks from last year's conference. Here’s another CppCon talk video we hope you will enjoy – and why not register today for CppCon 2024!

Lightning Talk: The Responsibility of C++ 

by Neil Henderson

Summary of the talk:

Hopefully an amusing and light-hearted look at C++ and its strengths and responsibilities in the software world from a recent life-changing experience.

Fat API Bindings of C++ Objects into Scripting Languages -- Russell K. Standish

By Blog Staff | Jul 16, 2024 03:30 PM | Tags: None

How do you expose a C++ object to a TypeScript layer or other scripting language? Russell K. Standish demonstrates an approach using a RESTService API that is scripting-language independent.

Fat API Bindings of C++ Objects into Scripting Languages

by Russell K. Standish

From the article:

A fat API exposes nearly all of a C++ object’s public attributes and methods to a consuming environment, such as a scripting language, or web client. This can be contrasted with a conventional, or thin API, where the API is defined up front, and the C++ object provides the implementation, most of which is private to the C++ layer.

Obviously, reflection is required to expose C++ objects to a consuming layer like this – this paper explores using the Classdesc system to implement reflection of C++ objects into a JavaScript/TypeScript environment via a REST service, and also via a Node.js API module.

2024-07 Mailing Available

By Administrator | Jul 16, 2024 02:14 PM | Tags: None

The 2024-07 mailing of new standards papers is now available.

CppCon 2023 std::linalg: Linear Algebra Coming to Standard C++ -- Mark Hoemmen

By Blog Staff | Jul 14, 2024 09:57 AM | Tags: None

Registration is now open for CppCon 2024! The conference starts on September 15 and will be held in person in Aurora, CO. To whet your appetite for this year’s conference, we’re posting videos of some of the top-rated talks from last year's conference. Here’s another CppCon talk video we hope you will enjoy – and why not register today for CppCon 2024!

CppCon 2023 std::linalg: Linear Algebra Coming to Standard C++

by Mark Hoemmen

Summary of the talk:

Many fields depend on linear algebra computations, which include matrix-matrix and matrix-vector multiplies, triangular solves, dot products, and norms. It's hard to implement these fast and accurately for all kinds of number types and data layouts. Wouldn't it be nice if C++ had a built-in library for doing that? Wouldn't it be even nicer if this library used C++ idioms instead of what developers have to do now, which is write nonportable, unsafe, verbose code for calling into an optimized Fortran or C library?

The std::linalg library does just that. It uses the new C++23 feature mdspan to represent matrices and vectors. The library builds on the long history and solid theoretical foundation of the BLAS (Basic Linear Algebra Subroutines), a standard C and Fortran interface with many optimized implementations. The C++ Standard Committee is currently reviewing std::linalg for C++26. The library already has two implementations that work with C++17 or newer compilers, and can take advantage of vendor-specific optimizations. Developers will see how std::linalg can make their C++ safer and more concise without sacrificing performance for use cases that existing BLAS libraries already optimize, while opening up new use cases and potential optimizations.

CppCon 2023 Spanny: Abusing C++ mdspan Is Within Arm’s Reach -- Griswald Brooks

By Blog Staff | Jul 12, 2024 01:52 PM | Tags: None

Registration is now open for CppCon 2024! The conference starts on September 15 and will be held in person in Aurora, CO. To whet your appetite for this year’s conference, we’re posting videos of some of the top-rated talks from last year's conference. Here’s another CppCon talk video we hope you will enjoy – and why not register today for CppCon 2024!

Lightning Talk: Spanny: Abusing C++ mdspan Is Within Arm’s Reach

by Griswald Brooks

Summary of the talk:

mdspan introduced in C++23 gave us a standard multidimensional way to view into a container of data. While the canonical use case is to refer to a stack or heap allocated data, the accessor policy allows you to inject any side effect allowing the data to come from anywhere... like a robot arm inspecting bins.