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carbon-language / carbon-lang

Carbon Language's main repository: documents, design, implementation, and related tools. (NOTE: Carbon Language is experimental; see README)
http://docs.carbon-lang.dev/
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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.

<img src="docs/images/quicksort_snippet.svg" align="right" width="575" alt="Quicksort code in Carbon. Follow the link to read more.">

Fast and works with C++

Modern and evolving

Welcoming open-source community

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:

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++:

Language Goals

We are designing Carbon to support:

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

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

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. You can see the demo interpreter for Carbon on compiler-explorer.com. We are also hard at work on a toolchain implementation with compiler and linker.

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:

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:

<img src="docs/images/cpp_snippet.svg" width="600" alt="A snippet of C++ code. Follow the link to read it.">

corresponds to this Carbon code:

<img src="docs/images/carbon_snippet.svg" width="600" alt="A snippet of converted Carbon code. Follow the link to read it.">

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:

<img src="docs/images/mixed_snippet.svg" width="600" alt="A snippet of mixed Carbon and C++ code. Follow the link to read it.">

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:

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:

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 demo interpreter for Carbon on: 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://github.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 "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://github.com/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:

Conference talks

Carbon focused talks from the community:

Upcoming

2024

2023

2022

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.

Contributing

You can also directly:

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