How C++ Finally Beats Rust at JSON Serialization

by Daniel Lemire & Francisco Geiman Thiesen

Summary of the talk:

JSON, or JavaScript Object Notation, has become a cornerstone for storing and exchanging data. Its appeal lies in its simplicity—human-readable text that elegantly captures structured data through attribute-value pairs and arrays: {"age": 5, "name": "Daniel", "toys": ["wooden dog", "little car"]}. JSON is intuitive yet powerful. But ingesting and producing JSON can turn into a performance choke point. In C++, it can be a tedious, error-prone task. Programmers wrestle with unexpected content, manually mapping data to and from native structures, all while striving for speed and safety.

With languages like Java, C#, Zig, Rust, or Python, JSON serialization and deserialization typically requires far less work. In particular, Rust's serde library blends convenience with high speed. We wish for a C++ library to automatically handle JSON production and consumption, seamlessly tied to native data structures. It is not merely to simplify life for developers; it is also about crafting code that is both fast and solid, generated at compile time by a battle-tested library.

Thankfully, C++ might soon be getting reflective metaprogramming (  PR2996  ). Leveraging the  experimental Bloomberg LLVM fork  with reflective metaprogramming, we have built a full-fledged implementation—complete with tests, benchmarks, and documentation. Our goal is to have production-ready code the moment mainstream compilers catch up. The results speak for themselves: we are parsing JSON directly into C++ structures at gigabytes per second, outpacing even mature heavyweights like Rust's serde. Better yet, the conversion between C++ data structures and JSON is fully automated, thanks to metaprogramming. It has the potential to be a leap forward for C++ in the data-driven age. Unfortunately, there are still problems and limitations: we present them and provide some solutions.

Trip report: June 2025 ISO C++ standards meeting (Sofia, Bulgaria)

by Herb Sutter

From the article:

A unique milestone: “Whole new language”

Today marks a turning point in C++: A few minutes ago, the C++ committee voted the first seven (7) papers for compile-time reflection into draft C++26 to several sustained rounds of applause in the room. I think Hana “Ms. Constexpr” Dusíková summarized the impact of this feature best a few days ago, in her calm deadpan way… when she was told that the reflection paper was going to make it to the Saturday adoption poll, she gave a little shrug and just quietly said: “Whole new language.”

Mic drop.

CppDevSurvey-2025-summary.pdf

A 100-page version of this report that also includes all individual write-in responses has now been forwarded to the C++ standards committee and C++ product vendors, to help inform C++ evolution and tooling.

Your feedback is valuable, and appreciated.

If you haven't already, please take 10 minutes to participate in this year's annual C++ developer survey! The results help to inform C++ standardization and C++ product vendors.

2025 Annual C++ Developer Survey "Lite"

The survey closes on Friday.

Thank you for participating and helping to inform our committee and community!

The annual global C++ developer survey is now open. As the name suggests, it's short:

2025 Annual C++ Developer Survey "Lite"

Please take 10 minutes or so to participate! A summary of the results, including aggregated highlights of common answers in the write-in responses, will be posted publicly here on isocpp.org and shared with the C++ standardization committee participants to help inform C++ evolution.

The survey closes in one week.

Thank you for participating and helping to inform our committee and community!

21st Century C++

by Bjarne Stroustrup

About the article:

Here, I present the key concepts on which performant, type safe, and flexible C++ software can be built: resource management, life-time management, error-handling, modularity, and generic programming. At the end, I present ways to ensure that code is contemporary, rather than relying on outdated, unsafe, and hard-to-maintain techniques: guidelines and profiles.

Contracts for C++ explained in 5 minutes

by Timur Doumler

From the article:

With P2900, we propose to add contract assertions to the C++ language. This proposal is in the final stages of wording review before being included in the draft Standard for C++26.

It has been suggested by some members of the C++ standard committee that this feature is too large, too complicated, and hard to teach. As it turns out, the opposite is true: contract assertions are actually very simple and can be explained in just five minutes. In this blog post, we will do exactly this!