rust-lang / rust-lang/rfcs

Consider making common traits object-safe

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Description

The following traits have Sized as a supertrait:

  • Clone
  • Default
  • From
  • FromStr
  • Into

The bound on the first four can be moved from the trait to a method-level where clause, while the bound on Into can be removed entirely.

Doing this has the benefit of allowing otherwise object-safe traits to use these as a supertrait, but has the drawback of being a breaking change (albeit one that I doubt affects much code).

These other traits also extend Sized, but are unstable:

  • One
  • Step
  • Zero

Contributor guide

No contributing guide indexed for this repository

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Review the listed traits and the proposed changes to their Sized bounds, then assess the compatibility tradeoff described in the issue. Done means reaching and documenting a decision on whether these common traits should become object-safe, including the unstable traits mentioned.

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
Clearly specified
Newbie friendliness
25/100

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