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The official repo for the design of the C# programming language
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C# Language Design

Welcome to the official repo for C# language design.

Design Process

C# is designed by the C# Language Design Team (LDT).

  1. To submit, support, and discuss ideas please subscribe to the language design mailing list.

  2. Ideas that the LDT feel could potentially make it into the language should be turned into proposals, based on this template, either by members of the LDT or by community members by invitation from the LDT. The lifetime of a proposal is described in proposals/ A good proposal should:

    • Fit with the general theme and aesthetic of the language.
    • Not introduce subtly alternate syntax for existing features.
    • Add a lot of value for a clear set of users.
    • Not add significantly to the complexity of the language, especially for new users.
  3. A prototype owner (who may or may not be proposal owner) should implement a prototype in their own fork of the Roslyn repo and share it with the design team and community for feedback. A prototype must meet the following bar:

    • Parsing (if applicable) should be resilient to experimentation--typing should not cause crashes.
    • Include minimal tests demonstrating the feature at work end-to-end.
    • Include minimal IDE support (keyword coloring, formatting, completion).
  4. Once a prototype has proven out the proposal and the proposal has been approved-in-principle by the design team, a feature owner (who may or may not be proposal or prototype owner(s)) implemented in a feature branch of the Roslyn repo. The bar for implementation quality can be found here.

  5. Design changes during the proposal or feature implementation phase should be fed back into the original proposal as a PR describing the nature of the change and the rationale.

  6. A PR should be submitted amending the formal language specification with the new feature or behavior.

  7. Once a feature is implemented and merged into shipping branch of Roslyn and the appropriate changes merged into the language specification, the proposal should be archived under a folder corresponding to the version of the language in which it was included, e.g. C# 7.1 proposals). Rejected proposals are archived under the rejected folder.

Language Design Meetings

Language Design Meetings (LDMs) are held by the LDT and occasional invited guests, and are documented in Design Meeting Notes in the meetings folder, organized in folders by year. The lifetime of a design meeting note is described in meetings/ LDMs are where decisions about future C# versions are made, including which proposals do work on, how to evolve the proposals, and whether and when to adopt them.

Language Specification

It is our plan to move the C# Language Specification into Markdown, and draft it in the spec folder. The spec drafts will eventually be standardized and published by ECMA. The folder currently contains an unofficial Markdown version of the C# 6.0 specification for convenience.


The reference implementation of the C# language can be found in the Roslyn repository. Until recently, that was also where language design artifacts were tracked. Please allow a little time as we move over active proposals.

DISCLAIMER: An active proposal is under active consideration for inclusion into a future version of the C# programming language but is not in any way guaranteed to ultimately be included in the next or any version of the language. A proposal may be postponed or rejected at any time during any phase of the above process based on feedback from the design team, community, code reviewers, or testing.

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