[swift-evolution] [Review #2] SE-0117: Default classes to be non-subclassable publicly

[John McCall]

> On Jul 16, 2016, at 12:59 AM, Xiaodi Wu via swift-evolution <swift-evolution at swift.org> wrote:
> 
> 
>         * What is your evaluation of the proposal?
> 
> This is improved from the previous iteration. The code example needs updating, as both instances of `open func bar()` should be `public open func bar()` as outlined in the Proposed Design section.

Good catch.  I'll fix this.
 
>         * Does this proposal fit well with the feel and direction of Swift?
> 
> Yes, mostly. There is one comment in the code example that describes a restriction which does not fit with the direction of Swift. It is not the main focus of the proposal but I think should be changed. Namely, the proposal comments:
> 
> "[The declaration `[public] open func bar()` inside a class not marked `open`] raises a compilation error: a method can't be marked `open` if the class it belongs to can't be subclassed."
> 
> This is discordant with the direction resolved by the core team in the SE-0025 revisions, where it was stated with regard to access modifiers:
> 
> "The compiler should not warn when a broader level of access control is used within a type with more restrictive access, such as `internal` within a `private` type. This allows the owner of the type to design the access they would use were they to make the type more widely accessible."
> 
> Applying the same rationale here would suggest that the compiler should not raise an error if a method is marked `open` inside a non-`open` type, in order to allow the owner of the type to design as though to make it subclassable without actually having to do so.

That's true.  We'll consider this.

John.

> 
>         * If you have used other languages or libraries with a similar feature, how do you feel that this proposal compares to those?
> 
> Yes, I've used OOP in other languages. As discussed, this approach is different from that taken by many of those but is a deliberate step.
>  
>         * How much effort did you put into your review? A glance, a quick reading, or an in-depth study?
> 
> Followed the discussion, read proposal carefully.
>  
> 
> More information about the Swift evolution process is available at
> 
>         https://github.com/apple/swift-evolution/blob/master/process.md <https://github.com/apple/swift-evolution/blob/master/process.md>
> 
> Thank you,
> 
> -Chris Lattner
> Review Manager
> 
> 
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