carbon lang

Carbon Language:
An experimental successor to C++

Why? |
Goals |
Status |
Getting started |
Join us

See our announcement video from
CppNorth. Note that Carbon is
not ready for use.

Fast and works with C++

• Performance matching C++ using LLVM, with low-level access to bits and
  addresses
• Interoperate with your existing C++ code, from inheritance to templates
• Fast and scalable builds that work with your existing C++ build systems

Modern and evolving

• Solid language foundations that are easy to learn, especially if you have
  used C++
• Easy, tool-based upgrades between Carbon versions
• Safer fundamentals, and an incremental path towards a memory-safe subset

Welcoming open-source community

• Clear goals and priorities with robust governance
• Community that works to be welcoming, inclusive, and friendly
• Batteries-included approach: compiler, libraries, docs, tools, package
  manager, and more

Why build Carbon?

C++ remains the dominant programming language for performance-critical software,
with massive and growing codebases and investments. However, it is struggling to
improve and meet developers\’ needs, as outlined above, in no small part due to
accumulating decades of technical debt. Incrementally improving C++ is
extremely difficult, both due to
the technical debt itself and challenges with its evolution process. The best
way to address these problems is to avoid inheriting the legacy of C or C++
directly, and instead start with solid language foundations like
modern generics system, modular code organization, and consistent,
simple syntax.

Existing modern languages already provide an excellent developer experience: Go,
Swift, Kotlin, Rust, and many more. Developers that can use one of these
existing languages should. Unfortunately, the designs of these languages
present significant barriers to adoption and migration from C++. These barriers
range from changes in the idiomatic design of software to performance overhead.

Carbon is fundamentally a successor language approach, rather than an
attempt to incrementally evolve C++. It is designed around interoperability with
C++ as well as large-scale adoption and migration for existing C++ codebases and
developers. A successor language for C++ requires:

• Performance matching C++, an essential property for our developers.
• Seamless, bidirectional interoperability with C++, such that a library
  anywhere in an existing C++ stack can adopt Carbon without porting the rest.
• A gentle learning curve with reasonable familiarity for C++ developers.
• Comparable expressivity and support for existing software\’s design and
  architecture.
• Scalable migration, with some level of source-to-source translation for
  idiomatic C++ code.

With this approach, we can build on top of C++\’s existing ecosystem, and bring
along existing investments, codebases, and developer populations. There are a
few languages that have followed this model for other ecosystems, and Carbon
aims to fill an analogous role for C++:

• JavaScript → TypeScript
• Java → Kotlin
• C++ → Carbon

Language Goals

We are designing Carbon to support:

• Performance-critical software
• Software and language evolution
• Code that is easy to read, understand, and write
• Practical safety and testing mechanisms
• Fast and scalable development
• Modern OS platforms, hardware architectures, and environments
• Interoperability with and migration from existing C++ code

While many languages share subsets of these goals, what distinguishes Carbon is
their combination.

We also have explicit non-goals for Carbon, notably including:

• A stable
  application binary interface
  (ABI) for the entire language and library
• Perfect backwards or forwards compatibility

Our detailed goals document fleshes out these ideas
and provides a deeper view into our goals for the Carbon project and language.

Project status

Carbon Language is currently an experimental project. We are hard at work on a
toolchain implementation with compiler and linker. You can try out the current
state at compiler-explorer.com.

We want to better understand whether we can build a language that meets our
successor language criteria, and whether the resulting language can gather a
critical mass of interest within the larger C++ industry and community.

Currently, we have fleshed out several core aspects of both Carbon the project
and the language:

• The strategy of the Carbon Language and project.
• An open-source project structure, governance model, and evolution process.
• Critical and foundational aspects of the language design informed by our
  experience with C++ and the most difficult challenges we anticipate. This
  includes designs for:
  • Generics
  • Class types
  • Inheritance
  • Operator overloading
  • Lexical and syntactic structure
  • Code organization and modular structure
• An under-development compiler and toolchain that will compile
  Carbon (and eventually C++ code as well) into standard executable code. This
  is where most of our current implementation efforts are directed.
  • Historically, there was also a prototype
    explorer interpreter that
    implemented an older version of the Carbon language design, but is no
    longer under development and has been archived.

If you\’re interested in contributing, we\’re currently focused on developing the
Carbon toolchain until it can
support Carbon ↔ C++ interop.
Beyond that, we plan to continue developing the design and toolchain until we
can ship the
0.1 language
and support evaluating Carbon in more detail.

You can see our full roadmap for more details.

Carbon and C++

If you\’re already a C++ developer, Carbon should have a gentle learning curve.
It is built out of a consistent set of language constructs that should feel
familiar and be easy to read and understand.

C++ code like this:

corresponds to this Carbon code:

You can call Carbon from C++ without overhead and the other way around. This
means you migrate a single C++ library to Carbon within an application, or write
new Carbon on top of your existing C++ investment. For example:

Read more about
C++ interop in Carbon.

Beyond interoperability between Carbon and C++, we\’re also planning to support
migration tools that will mechanically translate idiomatic C++ code into Carbon
code to help you switch an existing C++ codebase to Carbon.

Generics

Carbon provides a
modern generics system
with checked definitions, while still supporting opt-in
templates for seamless C++ interop. Checked
generics provide several advantages compared to C++ templates:

• Generic definitions are fully type-checked, removing the need to
  instantiate to check for errors and giving greater confidence in code.
  • Avoids the compile-time cost of re-checking the definition for every
    instantiation.
  • When using a definition-checked generic, usage error messages are
    clearer, directly showing which requirements are not met.
• Enables automatic, opt-in type erasure and dynamic dispatch without a
  separate implementation. This can reduce the binary size and enables
  constructs like heterogeneous containers.
• Strong, checked interfaces mean fewer accidental dependencies on
  implementation details and a clearer contract for consumers.

Without sacrificing these advantages, Carbon generics support
specialization, ensuring it can fully address performance-critical use cases
of C++ templates. For more details about Carbon\’s generics, see their
design.

In addition to easy and powerful interop with C++, Carbon templates can be
constrained and incrementally migrated to checked generics at a fine granularity
and with a smooth evolutionary path.

Memory safety

Safety, and especially
memory safety, remains a key
challenge for C++ and something a successor language needs to address. Our
initial priority and focus is on immediately addressing important, low-hanging
fruit in the safety space:

• Tracking uninitialized states better, increased enforcement of
  initialization, and systematically providing hardening against
  initialization bugs when desired.
• Designing fundamental APIs and idioms to support dynamic bounds checks in
  debug and hardened builds.
• Having a default debug build mode that is both cheaper and more
  comprehensive than existing C++ build modes even when combined with
  Address Sanitizer.

Once we can migrate code into Carbon, we will have a simplified language with
room in the design space to add any necessary annotations or features, and
infrastructure like generics to support safer design patterns.
Longer term, we will build on this to introduce a safe Carbon subset. This
will be a large and complex undertaking, and won\’t be in the 0.1 design.
Meanwhile, we are closely watching and learning from efforts to add memory safe
semantics onto C++ such as Rust-inspired
lifetime annotations.

Getting started

To try out Carbon immediately in your browser, you can use the toolchain at:
carbon.compiler-explorer.com.

We are developing a traditional toolchain for Carbon that can compile and link
programs. However, Carbon is still an early, experimental project, and so we
only have very experimental nightly releases of the Carbon toolchain available
to download, and only on limited platforms. If you are using a recent Ubuntu
Linux or similar (Debian, WSL, etc.), you can try these out by going to our
releases page and
download the latest nightly toolchain tar file:
carbon_toolchain-0.0.0-0.nightly.YYYY.MM.DD.tar.gz. Then you can try it out:

# A variable with the nightly version from yesterday:
VERSION=\"$(date -d yesterday +0.0.0-0.nightly.%Y.%m.%d)\"

# Get the release
wget https://*gi*thub.*com/carbon-language/carbon-lang/releases/download/v${VERSION}/carbon_toolchain-${VERSION}.tar.gz

# Unpack the toolchain:
tar -xvf carbon_toolchain-${VERSION}.tar.gz

# Create a simple Carbon source file:
echo \"import Core library \\\"io\\\"; fn Run() { Core.Print(42); }\" > forty_two.carbon

# Compile to an object file:
./carbon_toolchain-${VERSION}/bin/carbon compile \\
  --output=forty_two.o forty_two.carbon

# Install minimal system libraries used for linking. Note that installing `gcc`
# or `g++` for compiling C/C++ code with GCC will also be sufficient, these are
# just the specific system libraries Carbon linking still uses.
sudo apt install libgcc-11-dev

# Link to an executable:
./carbon_toolchain-${VERSION}/bin/carbon link \\
  --output=forty_two forty_two.o

# Run it:
./forty_two

As a reminder, the toolchain is still very early and many things don\’t yet work.
Please hold off on filing lots of bugs: we know many parts of this don\’t work
yet or may not work on all systems. We expect to have releases that are much
more robust and reliable that you can try out when we reach our
0.1 milestone.

If you want to build Carbon\’s toolchain yourself or are thinking about
contributing fixes or improvements to Carbon, you\’ll need to install our
build dependencies (Clang,
LLD, libc++) and check out the Carbon repository. For example, on Debian or
Ubuntu:

# Update apt.
sudo apt update

# Install tools.
sudo apt install \\
  clang \\
  libc++-dev \\
  libc++abi-dev \\
  lld

# Download Carbon\'s code.
$ git clone https://git*hub*.c*om/carbon-language/carbon-lang
$ cd carbon-lang

Then you can try out our toolchain which has a very early-stage compiler for
Carbon:

# Build and run the toolchain\'s help to get documentation on the command line.
$ ./scripts/run_bazelisk.py run //toolchain -- help

For complete instructions, including installing dependencies on various
different platforms, see our
contribution tools documentation.

Learn more about the Carbon project:

• Project goals
• Language design overview
• Carbon Toolchain
• FAQ

Conference talks

Carbon focused talks from the community:

2024

• Generic implementation strategies in Carbon and Clang, LLVM Developers\’
  Meeting (video,
  slides)
• The Carbon Language: Road to 0.1, NDC {TechTown}
  (video,
  slides)
• How designing Carbon with C++ interop taught me about C++ variadics and
  overloads, CppNorth (video,
  slides)
• Generic Arity: Definition-Checked Variadics in Carbon, C++Now
  (video,
  slides)
• Carbon: An experiment in different tradeoffs, panel session, EuroLLVM
  (video,
  slides)
  • Alex Bradbury\’s notes
• Carbon\’s high-level semantic IR lightning talk, EuroLLVM
  (video)

2023

• Carbon’s Successor Strategy: From C++ interop to memory safety, C++Now
  (video,
  slides)
• Definition-Checked Generics, C++Now
  • Part 1 (video,
    slides)
  • Part 2 (video,
    slides)
• Modernizing Compiler Design for Carbon’s Toolchain, C++Now
  (video,
  slides)

2022

• Carbon Language: Syntax and trade-offs, Core C++
  (video,
  slides)
• Carbon Language: An experimental successor to C++, CppNorth
  (video,
  slides)

Other videos

We additionally have toolchain videos.

Join us

We\’d love to have folks join us and contribute to the project. Carbon is
committed to a welcoming and inclusive environment where everyone can
contribute.

• Most of Carbon\’s design discussions occur on
  Discord.
• To watch for major release announcements, subscribe to our
  Carbon release post on GitHub
  and star carbon-lang.
• See our code of conduct and
  contributing guidelines for information about the Carbon
  development community.

Contributing

You can also directly:

• Contribute to the language design:
  feedback on design, new design proposal
• Contribute to the language implementation
  • Carbon Toolchain, and project infrastructure

You can check out some
\”good first issues\”,
or join the #contributing-help channel on
Discord. See our full
CONTRIBUTING documentation for more details.