Difficulties improving C++

C++ is the dominant programming language for the performance critical software our goals prioritize. The most direct way to deliver a modern and excellent developer experience for those use cases and developers would be to improve C++.

Improving C++ to deliver the kind of experience developers expect from a programming language today is difficult in part because C++ has decades of technical debt accumulated in the design of the language. It inherited the legacy of C, including textual preprocessing and inclusion. At the time, this was essential to C++’s success by giving it instant and high quality access to a large C ecosystem. However, over time this has resulted in significant technical debt ranging from integer promotion rules to complex syntax with “the most vexing parse”.

C++ has also prioritized backwards compatibility including both syntax and ABI. This is heavily motivated by preserving its access to existing C and C++ ecosystems, and forms one of the foundations of common Linux package management approaches. A consequence is that rather than changing or replacing language designs to simplify and improve the language, features have overwhelmingly been added over time. This both creates technical debt due to complicated feature interaction, and fails to benefit from on cleanup opportunities in the form of replacing or removing legacy features.

Carbon is exploring significant backwards incompatible changes. It doesn’t inherit the legacy of C or C++ directly, and instead is starting with solid foundations, like a modern generics system, modular code organization, and consistent, simple syntax. Then, it builds a simplified and improved language around those foundational components that remains both interoperable with and migratable from C++, while giving up transparent backwards compatibility. This is fundamentally a successor language approach, rather than an attempt to incrementally evolve C++ to achieve these improvements.

Another challenge to improving C++ in these ways is the current evolution process and direction. A key example of this is the committee’s struggle to converge on a clear set of high-level and long-term goals and priorities aligned with ours. When pushed to address the technical debt caused by not breaking the ABI, C++’s process did not reach any definitive conclusion. This both failed to meaningfully change C++’s direction and priorities towards improvements rather than backwards compatibility, and demonstrates how the process can fail to make directional decisions.

Beyond C++’s evolution direction, the mechanics of the process also make improving C++ difficult. C++’s process is oriented around standardization rather than design: it uses a multiyear waterfall committee process. Access to the committee and standard is restricted and expensive, attendance is necessary to have a voice, and decisions are made by live votes of those present. The committee structure is designed to ensure representation of nations and companies, rather than building an inclusive and welcoming team and community of experts and people actively contributing to the language.

Carbon has a more accessible and efficient evolution process built on open-source principles, processes, and tools. Throughout the project, we explicitly and clearly lay out our goals and priorities and how those directly shape our decisions. We also have a clear governance structure that can make decisions rapidly when needed. The open-source model enables the Carbon project to expand its scope beyond just the language. We will build a holistic collection of tools that provide a rich developer experience, ranging from the compiler and standard library to IDE tools and more. We will even try to close a huge gap in the C++ ecosystem with a built-in package manager.

Carbon is particularly focused on a specific set of goals. These will not align with every user of C++, but have significant interest across a wide range of users that are capable and motivated to evolve and modernize their codebase. Given the difficulties posed by C++’s technical debt, sustained priority of backwards compatibility, and evolution process, we wanted to explore an alternative approach to achieve these goals – through a backwards-incompatible successor language, designed with robust support for interoperability with and migration from C++. We hope other efforts to incrementally improve C++ continue, and would love to share ideas where we can.