[swift-evolution] [Pitch] Introducing role keywords to reduce hard-to-find bugs

[Adrian Zubarev]

I’d support the breaking change here to allow the language to evolve properly instead of introducing halve baked opt-ins and workarounds for issues that totally deserve a fix. The first thought that I had when reading the proposal the first time was, that extend does not add any benefit to the language and should be implicit by default, where on the other hand default solves a real problem we’re having today. David was quicker and pitched the ideal solution by making default necessary in Swift 4 which is a breaking change but it solves the issue nicely.

That said, personally I would not support the opt-in version.



-- 
Adrian Zubarev
Sent with Airmail

Am 16. Juni 2017 um 21:06:58, Paul Cantrell via swift-evolution (swift-evolution at swift.org) schrieb:


On Jun 16, 2017, at 1:14 PM, Erica Sadun via swift-evolution <swift-evolution at swift.org> wrote:

On Jun 16, 2017, at 8:44 AM, David Hart <davidhart at fastmail.com> wrote:

Okay, I undertand. I’m just worried that the proposal is a net negative if the keywords stay optional. I’ll mention it in more detail once we get to the review period.

Thanks for the work on the proposal!!

I believe a breaking change has little chance of being accepted at this point in the language lifecycle. Adding opt-in compiler auditing to increase safety is, IMO, a net positive. It's a deliberate trade-off. We have included other designs to allow the core team to choose an alternative they feel is best for the philosophy and direction of Swift. This doesn't close the door to future language releases enhancing the concept, phasing out the second keyword, or introducing keywords for additional safety auditing.

I find it a dangerous philosophy to insist that any new proposal be ideologically pure. Imperfect proposals can still improve the language within the realities of the timelines, user base, and code base of the Swift community.

-- E

I share David’s concern. I also tend to think Erica’s correct about breaking changes. If the core team says “go ahead and break it,” then I’m all for it, but that seems unlikely.

FWIW, if we’re sticking with the two-keyword approach, the language could emit warnings for _any_ extension members that aren’t marked with either `extend` or `default`.

P




On 16 Jun 2017, at 16:33, Erica Sadun <erica at ericasadun.com> wrote:

As we say in our introduction, we're pitching the most conservative approach. 

The proposal was designed for minimal language impact. It chooses a conservative approach that can be phased in first over time and language release over more succinct alternatives that would impact existing code bases.

We discuss the one keyword version (which most of us are a fan of) in the alternatives. The core team has to decide how much they're willing to allow existing code to warn and/or break, which is the consequence of the one keyword solution.

-- E

On Jun 16, 2017, at 7:44 AM, David Hart <davidhart at fastmail.com> wrote:

Erica, any thoughts on only having default and making it an error in a future version of Swift like was discussed on this thread? The idea seems to have a few supporters.

On 16 Jun 2017, at 15:33, Erica Sadun via swift-evolution <swift-evolution at swift.org> wrote:


On Jun 14, 2017, at 11:46 PM, Dave Abrahams via swift-evolution <swift-evolution at swift.org> wrote:


on Wed Jun 14 2017, Chris Lattner <swift-evolution at swift.org> wrote:

On Jun 14, 2017, at 10:11 AM, Erica Sadun via swift-evolution
<swift-evolution at swift.org> wrote:

Some pals and I have been kicking an idea around about introducing
better ways to support the compiler in protocol extensions. We want

to eliminate some hard-to-detect bugs. We've been brainstorming on
how to do this without affecting backward compatibility and
introducing a minimal impact on keywords.

We'd love to know what you think of our idea, which is to introduce
"role" keywords. Roles allow the compiler to automatically check the
intended use of a extension member definition against its protocol
declarations, and emit errors, warnings, and fixits as needed.  We
think it's a pretty straightforward approach that, if adopted,
eliminates an entire category of bugs.

The draft proposal is here:
https://gist.github.com/erica/14283fe18254489c1498a7069b7760c4
<https://gist.github.com/erica/14283fe18254489c1498a7069b7760c4>

Thanks in advance for your thoughtful feedback,

+1 on the idea of this.  

ditto.  IMO it also makes the protocol extension much more expressive
and easy to read.

--
-Dave


Pull request: https://github.com/apple/swift-evolution/pull/724

-- E

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