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

[Erica Sadun]

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 <mailto:swift-evolution at swift.org>> wrote:
>> 
>> 
>>> On Jun 14, 2017, at 11:46 PM, Dave Abrahams via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>> 
>>> 
>>> on Wed Jun 14 2017, Chris Lattner <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>> 
>>>>> On Jun 14, 2017, at 10:11 AM, Erica Sadun via swift-evolution
>>>>> <swift-evolution at swift.org <mailto: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>
>>>>> <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 <https://github.com/apple/swift-evolution/pull/724>
>> 
>> -- E
>> 
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> 

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