What Microsoft’s C# Journey Reveals About Open‑Source Language Evolution

Jared Parsons, who spent over 20 years at Microsoft and led the C# language team, shares insights from three recent podcast appearances, offering valuable lessons for technical team leaders.

Open Architecture

C# was created at Microsoft in 2000 and open‑sourced in 2014. The entire compiler ecosystem, including debugging tools and Visual Studio features, is now open source.

Parsons notes that moving to GitHub required a cultural shift toward openness and the removal of non‑open‑source dependencies.

Compiler as API

The compiler team provides a library API that lets developers inspect code, generate diagnostics, and integrate with IDEs. This API underpins Visual Studio and other Microsoft tools, enabling a rich ecosystem of extensions and analyzers.

Parsons describes the compiler as a "library of a thousand lines of code" that interacts heavily with servers, and emphasizes that exposing it as an API makes the language more extensible.

Testing at Scale

The team runs extensive automated testing, merging pull requests every four hours and producing a new compiler build within eight hours, which then powers Visual Studio.

Each pull request triggers roughly 750,000 tests across multiple platforms and architectures, ensuring reliability for the many Azure services built on C#.

Language Design as Art

Parsons discusses the artistic aspect of language design, balancing performance improvements (such as Span and zero‑allocation calls) with aesthetic considerations.

He highlights that while compiler engineering is straightforward, creating a beautiful, usable language is a challenging art.

Future of C#

Microsoft continues to invest in performance features, such as improving Span and adding productivity enhancements with implicit and explicit extensions.

Parsons emphasizes that language decisions are influenced by competing ecosystems and that the success of a language depends on its surrounding toolchain.

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