Proposal: Improve Crash-Safety when Importing Objective-C Code Without Nullability Attributes (former: Import as Optional by Default)

[fabb]

This proposal was discussed before on the swift-evolution mailing list with the topic Improve Crash-Safety when Importing Objective-C Code Without Nullability Attributes. Most of the feedback was positive.

In the proposal, 2 solutions are presented. As there has not yet been enough feedback on which solution was to prefer, I thought it was best to put them both into one proposal and have the reviewers decide.

I can be contacted via the swift-evolution mailing list, or comments on this pull request.
https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151207/001054.html

Looking forward to the review! :-)

[radex]

IMHO it would be a good idea to squash those commits — having 15 commits for a single thing gets noisy in git history.

[DougGregor]

Yes, please squash this.

[fabb]

Ok done, squashed and rebased on master.

[fabb]

Ok, seems like when squashing/rebasing commits, code reviews get lost here on github, so I'll rather avoid squashing/rebasing.

[DougGregor]

The core team has discussed this, and we are going to close this pull request. For one, a specific proposal should be just that: one specific proposal. The public review isn't to decide among alternatives, it is to evaluate a complete design. In this case, neither solution is acceptable:

Solution #1 introduces a significant burden on programmers that use non-nullability-annotated C and Objective-C APIs. Implicitly unwrapped optionals were introduced precisely because non-nullability-annotated C and Objective-C APIs are prevalent (and will continue to be so for many years), and the cost of turning all of the implicitly-unwrapped optionals into true optionals (in terms of extra if-lets, !'s, etc.) is significant.

Solution #2 is asking for a warning, which is outside the scope of the Swift evolution process.

[fabb]

The follow-up compiler feature request for adding warnings can be found here: https://bugs.swift.org/browse/SR-104