[swift-evolution] [Proposal] Sealed classes by default

[Sean Heber]

Ok, I suppose that this design *basically* undoes the sealed by default thing, doesn’t it? :P  lol. One of those days, I guess..

Sigh.

Crawling away…

l8r
Sean


> On Jul 1, 2016, at 1:16 PM, Sean Heber <sean at fifthace.com> wrote:
> 
> Coming in late on this, but here’s my take guided by the principal of least surprise (according to me):
> 
> - everything is sealed within its module by default, no keyword
> - use “public” to mean “exported out of the module, subclass/overridable”
> - use “public(final)” to mean “exported out of the module, no subclassing or overriding externally, but overriding and subclasses allowed internally”
> - meaning of “final” does not change
> - using “public final” then means the same as both public(final) and also “final” internal to the module
> - using “public(final) final” could be presented as an error with fixit since it’s redundant
> 
> Did I miss anything?
> 
> l8r
> Sean
> 
> 
> 
>> On Jul 1, 2016, at 12:53 PM, John McCall via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>>> On Jul 1, 2016, at 10:51 AM, Michael Ilseman <milseman at apple.com> wrote:
>>> If “opened”, who or what did the opening? If “open” is like “extensible”, then I would interpret “opened” to be like “extended”.
>> 
>> Yeah, I would prefer "open" to "opened".
>> 
>> John.
>> 
>>> 
>>>> On Jul 1, 2016, at 10:35 AM, Leonardo Pessoa via swift-evolution <swift-evolution at swift.org> wrote:
>>>> 
>>>> The proposal was to use "sealed" so why not "opened"? I understand it
>>>> may not be common to use "opened" as an adjective but from the
>>>> dictionaries I consulted it is possible to.
>>>> 
>>>> opened class MyViewController: UIViewController {
>>>>    opened func displayMe(_ me: person) { … }
>>>> }
>>>> 
>>>> On 1 July 2016 at 13:47, John McCall via swift-evolution
>>>> <swift-evolution at swift.org> wrote:
>>>>> On Jul 1, 2016, at 12:23 AM, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:
>>>>> That starts to look an awful lot like a fifth access level just for classes
>>>>> (I know you're not proposing one, but it could start to look that way to a
>>>>> user). I think there's much to be said for having the word public in front
>>>>> of things that are public. Unless, of course, your strawman keyword is a
>>>>> much maligned compound word that begins with "public", like
>>>>> "publicoverridable".
>>>>> 
>>>>> 
>>>>> I would also prefer a single keyword if the word implies something about
>>>>> accessibility.  "open" does that, although using it here would conflict with
>>>>> its potential use on enums unless we required all cases within the defining
>>>>> module to be present in the enum declaration rather than extensions.
>>>>> 
>>>>> I don't think we'd ever use a compound keyword that starts with public; we'd
>>>>> just separate them and say that the second half can only be present on a
>>>>> public declaration, or do this parenthesized syntax.
>>>>> 
>>>>> John.
>>>>> 
>>>>> 
>>>>> On Fri, Jul 1, 2016 at 01:54 Brent Royal-Gordon <brent at architechies.com>
>>>>> wrote:
>>>>>> 
>>>>>>> If we're going to go along those lines, we should just use
>>>>>>> public(subclassable) and public(overridable).  We can fall back on those if
>>>>>>> necessary; I would just like to continue looking for better alternatives.
>>>>>> 
>>>>>> I would prefer to have a *single* keyword which meant both public and
>>>>>> overridable. That would minimize the impact of this feature—instead of
>>>>>> writing:
>>>>>> 
>>>>>>     public class MyViewController: UIViewController {
>>>>>>             public func displayMe(_ me: person) { … }
>>>>>>     }
>>>>>> 
>>>>>> You'd write (strawman keyword):
>>>>>> 
>>>>>>     openseason class MyViewController: UIViewController {
>>>>>>             openseason func displayMe(_ me: person) { … }
>>>>>>     }
>>>>>> 
>>>>>> And then `MyViewController` could be subclassed, and `displayMe`
>>>>>> overridden.
>>>>>> 
>>>>>> --
>>>>>> Brent Royal-Gordon
>>>>>> Architechies
>>>>>> 
>>>>> 
>>>>> 
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