Skip to content

Stabilizable subset of const generics #332

Closed
@withoutboats

Description

@withoutboats

Proposal

We should create a new feature min_const_generics, which contains a subset of the const generics feature suitable for stabilization.

This will impose two restrictions on const generics:

  1. They can only have the type of an integral primitive type (integers, bool, and char).
  2. Expressions used in const generic position must be either:
    • Just a const generic name in scope (e.g. N)
    • A const expression which contains on no free type or const parameters.

The latter will be implemented simply syntactically: if an expression contains a type or const parameter in its macro-expanded AST, it will error, unless it is just the name of a const generic.

This feature will not depend on lazy normalization of consts.

Mentors or Reviewers

@eddyb @varkor @oli-obk

Process

The main points of the Major Change Process is as follows:

  • File an issue describing the proposal.
  • A compiler team member or contributor who is knowledgeable in the area can second by writing @rustbot second.
    • Finding a "second" suffices for internal changes. If however you are proposing a new public-facing feature, such as a -C flag, then full team check-off is required.
    • Compiler team members can initiate a check-off via @rfcbot fcp merge on either the MCP or the PR.
  • Once an MCP is seconded, the Final Comment Period begins. If no objections are raised after 10 days, the MCP is considered approved.

You can read more about Major Change Proposals on forge.

Comments

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.

Metadata

Metadata

Assignees

No one assigned

    Labels

    T-compilerAdd this label so rfcbot knows to poll the compiler teammajor-changeA proposal to make a major change to rustcmajor-change-acceptedA major change proposal that was accepted

    Type

    No type

    Projects

    No projects

    Milestone

    No milestone

    Relationships

    None yet

    Development

    No branches or pull requests

    Issue actions