Sealing classes by default is a terrible idea IMHO. Fortunately, my faith in
the Swift core team is strong enough so that I cannot believe that this has a
chance of ever being implemented at all :)
Why do I think it's terrible? I do subclass classes even when they say that you
shouldn't do it. I even monkey-patched a few classes in the past. Why? Not
because I prefer hacking over clean coding, but to get the job done. Every few
months or so I encounter a situation where such hacking attempts are the only
feasible way to make something work. Or I use them during research activities
or unofficial "feasibility studies". (If that's not the case for you, then
maybe you are working in a different job than I. Monkey patching is rarely
necessary if you make iPhone apps.) These are situations where everyone else
just says "that's not possible". Yes, you can make that USB driver class stop
spamming the console; yes, you can stop that library from crashing randomly.
There is so much more to say on this topic. Sealing classes is also bad because
it prevents forms of experimental coding. It doesn't solve a real problem. How
often have I seen bugs where someone subclassed a class that shouldn't be
subclassed? That's so rare. But if all classes are sealed by default this will
lead to far worse problems. When a developer subclasses a class, he usually has
a reason. There already is a `final` keyword in Swift, and a dev really thinks
that a class shouldn't be subclass-able, he can use it already. And if I
subclass it from Objective-C anyways, then maybe I know what I'm doing?
And I'm not buying this "performance" argument. If you want better performance,
write the hot functions in C or maybe even in assembler. The dynamic dispatch
overhead is not the feature that makes programs bad or slow. It's quadratic
algorithms (e.g. unnecessary nested loops), calling functions multiple times
(e.g. if(a.foo.bar(x[2]) == "joo" || a.foo.bar(x[2]) == "fooo" ||
a.foo.bar(x[2]) == nil) { ... }), or just overly complex code: all of them have
more impact than dynamic dispatch. Even worse for performance is unnecessary IO
or using graphics APIs inefficiently. A good profiler can help a lot with these
issues.
Swift should be designed for the real world, not for an ideal world that does
not exist and that will never exist.
-Michael
> Am 28.06.2016 um 15:09 schrieb L. Mihalkovic via swift-evolution
> <[email protected]>:
>
>
> Regards
> LM
> (From mobile)
>> On Jun 28, 2016, at 1:57 PM, Alejandro Martinez via swift-evolution
>> <[email protected]> wrote:
>>
>> Anton Zhilin: That is one of the points if I’m not mistaken. Sealed
>> means that with whole-module-optimization the compiler can optimise
>> more things as it can treat it as final for other modules.
>>
>> L. Mihalkovic: Could you give an example of what exactly do you mean?
>> I know one of the reasons behind the proposal is to actually improve
>> those situations by forcing us to think more on customisation when
>> designing APIs.
>
> In many situation it has been my experience that libraries can be extended
> DESPITE their authors, rather than only thanks to the skills the authors
> have shown in planning for the future. It is what happened to me with
> AlamoFire, where i was able to extend it because some cracks existed which
> let me do something the designers did not think about (to me it was a lack of
> imagination to not have anticipated what i wanted to do).
>
> So if this can happen with a lib made by very experienced/talented
> developers, then imagine what happens with far less skilled developers.. it
> will mean having to copy code in order extend. It may sound pessimistic, but
> if u had seen as much bad code as i have seen, you might understand the view
> i am sharing.
>
> What's worse is that objc is not particularly conducive to good software
> architecture (it is a bit like perl and javascript where anything can be
> touched from anywhere, and has a limited set of constructs compared to c++,
> scala, java, c#, swift). So i do not believe that it has prepared objc devs
> to suddenly become great code designers with a language that has multiples
> levels of scoping/nesting (i would not use most of the swift libs i have seen
> on github to teach software design).
>
> Hence my conclusion that defaulting to sealed may be giving too much credit
> to the code that is currently available for reuse.
>
>
>>
>> On Tue, Jun 28, 2016 at 12:44 PM, Anton Zhilin via swift-evolution
>> <[email protected]> wrote:
>>> Does `sealed` allow for any optimizations? Maybe somehow devirtualizing
>>> method calls?
>>>
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>>
>>
>>
>> --
>> Alejandro Martinez
>> http://alejandromp.com
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