Use concepts with std::remove_cvref_t -- Sandor Dargo

By Blog Staff | Sep 23, 2025 03:16 PM | Tags: None

Let’s talk about templates, constraints, and concepts. We’ll start with a quick reminder of why concepts are essential when working with templates. Then we’ll dive into the challenge posed by reference-qualified types and finish with a practical solution.

Use concepts with std::remove_cvref_t

by Sandor Dargo

From the article:

By now, it’s well known that using unconstrained templates is discouraged. Even the C++ Core Guidelines strongly recommend against it.

T.47 only advises avoiding highly visible unconstrained templates with common names due to the risks of argument-dependent lookup going wrong. T.10 goes further, recommending that we specify concepts for every template argument to improve both simplicity and readability.

The same idea appears in I.9, which suggests documenting template parameters using concepts.

It’s hard to argue with these guidelines. Concepts make code more readable — just by looking at a function, class, or variable template, the reader can immediately tell what kinds of types are accepted.

If you want to learn more about concepts, check out my concepts-related articles or my book on concepts.

But what makes a good concept? That’s a more complex topic — and one we can’t fully cover in a single article.

Simple Compile-Time Dynamic Programming in Modern C++ -- Andrew Drakeford

By Blog Staff | Sep 19, 2025 03:14 PM | Tags: None

Compile time code can be very efficient. Andrew Drakeford demonstrates how to write efficient chains of matrix multiplication.

Simple Compile-Time Dynamic Programming in Modern C++

by Andrew Drakeford

From the article:

Modern C++ enables us to solve mathematical optimisation problems at compile time. With the expanded constexpr capabilities [Fertig21, Turner18, Turner19, Wu24], we can now write clear and efficient optimisation logic that runs during compilation. Fixed-size containers such as std::array fit naturally into these routines. Even standard algorithms, such as std::sort and std::lower_bound, are now constexpr, enabling more straightforward code and more powerful compile-time computations. Additionally, compile-time optimisation generates constant results, which enables the compiler to create even more efficient code. We will use the matrix chain multiplication problem as our worked example.

Matrix chain multiplication

Matrix chain multiplication is a classic dynamic programming problem [Corman22, Das19, Mount]. It aims to determine the most efficient method for multiplying a sequence of matrices. Since matrix multiplication is associative, the order of grouping does not affect the result. However, the number of scalar multiplications involved can vary depending on the grouping.

Consider the three matrices A₁ (10×100), A₂ (100×5), and A₃ (5×50), multiplied in a chain, A₁ × A₂ × A₃.

There are two ways to multiply them:

1. Grouping as (A₁ × A₂) × A₃ first computes a 10×5 matrix, then multiplies that with A₃. This results in 5,000 operations for the first multiplication, and another 2,500 for the second – a total of 7,500 scalar multiplications.
2. Grouping as A₁ × (A₂ × A₃) first multiplies A₂ and A₃, then A₁. This results in 25,000 operations for the first step and 50,000 for the second – a total of 75,000, which is clearly worse.

C++26 reflection at compile-time -- Andreas Fertig

By Blog Staff | Sep 17, 2025 03:09 PM | Tags: None

In today's post, I like to talk about C++26 and one of the probably most impactful features that have been added to the working draft. While C++26 is still some months away from official completion, since the WG21 summer meeting in June we all now know what will be in C++26.

C++26 reflection at compile-time

by Andreas Fertig

From the article:

While the new standard will have plenty of great improvements the one that will most likely change a lot is reflection at compile-time! In Sofia we voted seven reflection papers into C++26:

• P1306R5 Expansion statements
• P2996R13 Reflection for C++26
• P3096R12: Function parameter reflection in reflection for C++26
• P3293R3: Splicing a base class subobject
• P3394R4: Annotations for reflection
• P3491R3: define_static_
• P3560R2: Error handling in reflection

The papers above should give you enough to read for your vacation. I'll leave that theoretical study up to you for now.

Let's talk practical

The main question is, what can you do with that new feature? Well, I'm not the first one who published their ideas.

Format your own type (Part 2) -- Sandor Dargo

By Blog Staff | Sep 15, 2025 03:06 PM | Tags: None

Previously, we discussed how to write our own formatter and finished with a relatively simple solution for printing a struct called ProgrammingLanguage. Today, we’ll take it to the next level.

Format your own type (Part 2)

by Sandor Dargo

From the article:

Add more options for semantic versioning

Let’s dream big. Instead of only handling major and minor versions (like Python 3.12), let’s aim to fully support semantic versioning.

Semantic versioning (SemVer) is a versioning scheme that conveys meaning about the underlying changes in a release. It typically consists of three parts: MAJOR.MINOR.PATCH.

We should be able to print all these correctly:

ProgrammingLanguage cpp{"C++", 20};
ProgrammingLanguage python312{"Python", 3, 12};
ProgrammingLanguage python31211{"Python", 3, 12, 11};


std::cout << std::format("{:%n%v} is fun", cpp) << '\n';  // C++20 is fun
std::cout << std::format("{:%n %v} is fun", python312) << '\n';  // Python 3.12 is fun
std::cout << std::format("{:%n %v} is fun", python31211) << '\n';  // Python 3.12.11 is fun

CppCon 2025 The Programmer CEO -- Greg Law

By Blog Staff | Sep 12, 2025 01:46 PM | Tags: None

Registration is now open for CppCon 2025! The conference starts on September 13 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 2025!

The Programmer CEO

Wednesday, September 17 16:45 - 17:45 MDT

by Greg Law

Summary of the talk:

Many programmers think about starting a company. It’s often not about getting rich so much as to pursue a vision for a computer program that is much bigger than one person could write alone. Like most programmers who start up, I had no formal training and little experience outside of software development. I was naively confident, and didn’t know what I didn’t know (it turned out that that was a LOT!)

The talk includes some of the lessons I’ve learned along the way, many of which were a complete surprise. I’ll cover getting investment, building the product, building a team, and getting and keeping customers. Little of this talk is directly about programming, but it is aimed at programmers who want to create code in order to create a business, or who want to create a business so that they can create the code they want.

Much of the content is also relevant for programmers who find themselves doing non-programming tasks, such as managing people or customer-facing roles, and anyone working at a start-up. Contains candid, warts-and-all war stories, and because it’s for programmers, comes with a no adverts and no business-talk BS guarantee.

Greg is co-founder and CEO at Undo. He is a programmer at heart, but likes to keep one foot in the software world and one in the business world. Greg finds it particularly rewarding to turn innovative software technology into a real business. Greg has over 25 years' experience in innovative start-up software companies.

CppCon 2025 Engineers Are Users Too: Case Study in Design Thinking for Infrastructure -- Grace Alwan

By Blog Staff | Sep 11, 2025 01:42 PM | Tags: None

Registration is now open for CppCon 2025! The conference starts on September 13 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 2025!

Engineers Are Users Too: A Case Study in Design Thinking for Infrastructure

Tuesday, September 16 15:15 - 16:15 MDT

by Grace Alwan

Summary of the talk:

Bringing together strong engineering skills with a foundation in UX Design can open unexpected doors—especially in fields like infrastructure, where there are few engineers trained in design. As a software engineer on an infrastructure team at a fintech company, I work on low-level systems that power how engineers manage compute at scale. But it’s my background in UX and human-computer interaction that’s made me an invaluable asset. By applying design thinking to infrastructure – through prototyping, user interviews, and iteration – I transformed a complex internal workflow and quickly became a subject matter expert.

This talk will walk you through that journey and give you the tools to be a design trailblazer in your own career. You'll leave with practical techniques for integrating empathy and user-centric thinking into deeply technical work—and insights on how expanding your skillset can accelerate your growth as a C++ or systems engineer.

Grace Alwan graduated from Stanford University in 2023, where she got her BS and MS in Computer Science specializing in Human-Computer Interaction. She is now a software engineer in the Technology Infrastructure org at Bloomberg, where she works on cluster and host management.

2025-09 Mailing Available

By Administrator | Sep 11, 2025 11:08 AM | Tags: None

The 2025-09 mailing of new standards papers is now available.

Planning the next Meeting C++ job fairs

By Meeting C++ | Sep 11, 2025 09:00 AM | Tags: meetingcpp jobs events community

Meeting C++ is hosting a job fair in October online and planning a job fair in November in Berlin at Meeting C++ 2025!

Planning the next Meeting C++ job fairs

by Jens Weller

From the article:

The next Meeting C++ online job fair is planned for October 14th & 15th, also I'd like to talk about the onsite job fair plans for Meeting C++ 2025!

If you have open positions you should advertise them in the bi-weekly Meeting C++ Jobs Newsletter, which now also powers the candidate listing of Meeting C++ with 80+ international candidates at the moment.

 

Format your own type (Part 1) -- Sandor Dargo

By Blog Staff | Sep 10, 2025 08:01 PM | Tags: None

I recently published two posts about how C++26 improves std::format and the related facilities. (If you missed them, here are Part 1 and Part 2). Now it’s time to explore how you can format your own types using std::format.

Format your own type (Part 1)

by Sandor Dargo

From the article:

std::format was introduced in C++20 and is based on Victor Zverovich’s <fmt> library, which in turn was inspired by Python’s string formatting capabilities.

Let’s skip the fancy formatting options and simply see how to interpolate values using std::format.

#include <format>
#include <iostream>
#include <string>

int main() {
    std::string language{"C++"};
    int version{20};
    std::cout << std::format("{}{} is fun", language, version) << '\n';
}

/*
C++20 is fun
*/

That was easy.

Now imagine you want to print your own type. That won’t work by default.

CppCon 2025 Changing /std:c++14 to /std:c++20 - How Hard Could It Be? -- Keith Stockdale

By Blog Staff | Sep 10, 2025 01:40 PM | Tags: None

Registration is now open for CppCon 2025! The conference starts on September 13 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 2025!

Changing /std:c++14 to /std:c++20 - How Hard Could It Be?

Monday, September 15 15:15 - 16:15 MDT

by Keith Stockdale

Summary of the talk:

Rare put in huge amounts of work to bring Sea of Thieves to PlayStation 5 and to upgrade from the old XDK and UWP platforms to the new GDK platform. In this session, Rare will discuss why they made the decision to take this opportunity to also upgrade from C++14 to C++20. It shouldn’t be much harder than changing a 14 to a 20, right? How hard could it be?

Rare will discuss all the work that was involved in upgrading their language standard and share some anecdotes of some of the challenges that were met along the way. They will go through the benefits that they have felt from this upgrade along with some plans for continuing this work in the future.

Keith Stockdale is a Northern Irish senior software engineer who has been working on the Engine and Rendering teams at Rare Ltd for the last 8 years working on Sea of Thieves. At Rare, Keith's main areas of focus are involved in maintaining and creating general purpose simulations that run on the GPU. For example, he is the owner of the GPU particle system that drives the visual effects in Sea of Thieves. Keith is enthusiastic about promoting writing good quality code, whether it is running on the CPU on the GPU. He is driven towards ensuring that the code-bases he works in are enjoyable to work in for all current and future developers on his team.