[swift-evolution] [Proposal Draft] Remove open Access Modifier

Charlie Monroe charlie at charliemonroe.net
Wed Feb 22 01:29:10 CST 2017

> On Feb 22, 2017, at 8:15 AM, Jean-Daniel via swift-evolution <swift-evolution at swift.org> wrote:
>> Le 21 févr. 2017 à 17:19, Tino Heth via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> a écrit :
>>> I’ll concede that the proposal makes a claim that might very well be disproved. I would very much like to see an actual example of a public class that **has** to be public but **shouldn’t** be open for obvious reasons. I would happily accept being shown wrong on that point.
>> This is afaics one of the most active disputes on evolution — and you can save you a lot of grief by accepting that it is pointless:
>> The whole discussion isn't based on facts at all, despite many false claims that marking things as final is generally better.
>> I have asked for a single example to prove this in the past as well, so I guess no one can present such a thing to you.

To me, the largest purpose is when you have a root class ("abstract") and a few subclasses that represent various options - in Scala, this would be a case class. For various reasons, it can't be an enum - for example, you need a lot of stored data and an enum case a(Int, Int, Int, Bool, Int, Double) is not very usable.

In certain places, you can have switches based on the actual subtype - with the default case causing fatalError. In such case, you definitely don't want additional subclasses to exist outside of the module as it would break the assumption of a known number of subclasses.

You can't make the root class final since you inherit from it. In such case, the public modifier makes sense.

> This is bad faith. The original discussion contains many real life example. You just don’t want to admit open is useful for many library writers.
>> It is personal preference, so arguments don't help much here.
>> Maybe it helps to know the whole story, as everything started with "final should be default", followed by a try to forbid subclassing for types from a different module by default, finally arriving at the current compromise where you have to decide wether module clients should be allowed to subclass or not.
>> Nobody ever requested that public should be the only access level, so there has been only been pressure applied from one direction — it's interesting to see some backlash now.
>> Imho people already were quite tired of discussion when public/open was accepted as a compromise...
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