<variant>: variant should store its index as an unsigned type
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Description
@CaseyCarter explained:
"variant should store its index as an unsigned type biased by +1, so the "valueless" index is 0. index() will become slightly more expensive, since we must decrement the stored value instead of the current sign-extension. All other operations will become cheaper, since they currently add 1 to bias the index anyway."
Also tracked by Microsoft-internal VSO-659268 / AB#659268.
vNext note: Resolving this issue will require breaking binary compatibility. We won't be able to accept pull requests for this issue until the vNext branch is available. See #169 for more information.
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
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- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reviewing the issue rationale and the information in #169 about the vNext branch and binary compatibility. The intended result is unsigned, +1-biased variant index storage with 0 representing valueless, while index() decrements the stored value; no files or tests are named here.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- cpp
- Domain
- compilers
- Issue type
- Refactor
- Difficulty
- 5/5
- Estimated time
- Over a week
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 20/100