[swift-evolution] Abstract methods

[Lance Parker]

How would a class partially implement a protocol? That’s a compile error.

> On Nov 2, 2017, at 2:30 PM, C. Keith Ray via swift-evolution <swift-evolution at swift.org> wrote:
> 
> If a class partially implemented a protocol, it also would not be instantiatable, but a subclass can supply the missing method(s). Doesn’t the compiler already handle that? How are abstract classes harder?
> 
> C. Keith Ray
> https://leanpub.com/wepntk <https://leanpub.com/wepntk> <- buy my book?
> http://agilesolutionspace.blogspot.com/ <http://agilesolutionspace.blogspot.com/>
> twitter: @ckeithray
> http://www.thirdfoundationsw.com/keith_ray_resume_2014_long.pdf <http://www.thirdfoundationsw.com/keith_ray_resume_2014_long.pdf>
> 
> On Nov 2, 2017, at 2:22 PM, Slava Pestov <spestov at apple.com <mailto:spestov at apple.com>> wrote:
> 
>> Abstract methods and classes seem like they will introduce a fair amount of complexity in the type checker, particularly around metatypes and constructors, because now we have this new concept of a class that cannot be directly instantiated. I’m not sure the cost is worth the benefit.
>> 
>> Slava
>> 
>>> On Nov 2, 2017, at 12:45 PM, C. Keith Ray via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>> 
>>> How many "subclass must override" assertions or comments in base class methods do we need to see, to want to add "abstract" to the Swift language? 5? 50? 500?
>>> 
>>> It's a not uncommon idiom in Objective-C.
>>> 
>>> I'm about to port a substantial amount of C++ code to swift, and compiler help to enforce abstract classes would be very useful.
>>> 
>>> 
>>> --
>>> C. Keith Ray
>>> Senior Software Engineer / Trainer / Agile Coach
>>> * http://www.thirdfoundationsw.com/keith_ray_resume_2014_long.pdf <http://www.thirdfoundationsw.com/keith_ray_resume_2014_long.pdf>
>>> 
>>> 
>>> 
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>> 
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