[swift-evolution] Add code to super methods.

Dave Abrahams dabrahams at apple.com
Tue Nov 29 09:05:35 CST 2016

> On Nov 29, 2016, at 1:48 AM, Tino Heth <2th at gmx.de> wrote:
>> Methods that need to be called when they are overridden are
>> almost always a result of poor design.
> Without an explanation or data to back this statement, it's hard to argue about it, and I won't make random shots. 
> But as a matter of fact, we have to deal with methods which require the behaviour in question now, and I have no idea when Cocoa will be replaced with something better.

That's a great point.  I just don't want to punish those who create methods with default implementations that are designed to be completely replaced in subclasses.  I suppose that *could* encourage more use of protocols, but that seems like a very unfriendly way to reach a protocol-oriented utopia  ;-)

> Just out of sheer curiosity:
> What would be a better design for a method like viewWillAppear? The obvious alternative that is possible with current Swift and template methods looks really ugly to me:
> Not only would you have to add two empty methods to each subclass of UIViewController,

Why two, and why empty?  UIViewController would supply its own empty default implementation.

> but also rely on that those methods are only overridden once in the hierarchy of inheritance.

There's no law saying you *can't* call super if you absolutely must build a two-level hierarchy below UIViewController (though there are ways around that—the main one being to avoid inheritance hierarchies).  I just don't want to create a world where you're always expected to call super everywhere, which is what would happen if we always warn when you don't call super.
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