rust-lang / rust-lang/rfcs

RFC: Coercible and HasPrefix for Zero Cost Coercions

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A-coercions postponed T-lang
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Description

This is largely based on (with lots of copied text) @glaebhoerl's proposal in mozilla/rust#9912, but with a few changes:

  • I formalized the idea of "contexts" by using GHC's roles.
  • I used this role system to include user-defined pointers and data structures.
  • I dropped contravariance for simplicity. This may have been a bad idea, but it's unclear how useful contravariance is.

Tracking issue for postponed PR #91

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  3. Fork the repository and make your change on a branch.
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Research direction

Start by reading this RFC alongside the referenced mozilla/rust#9912 proposal and the postponed PR #91. Review how the RFC defines contexts with GHC's roles, user-defined pointers and data structures, and the decision to omit contravariance. Done means resolving the proposal's open design questions and determining the status or next step for PR #91.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
compilers
Issue type
Feature
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
20/100

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