[swift-evolution] Final by default for classes and methods

Kevin Lundberg kevin at klundberg.com
Mon Dec 7 13:21:52 CST 2015

Resending to whole list:

I can appreciate the desire for this, but I would not support it personally. In a former life developing C# code where this is the default behavior, I wanted to extend a class's behavior to make it work slightly differently, but since everything is final by default (sealed in C# parlance) I was prevented from doing so. The scope of my change was minimal and well defined, and it would not have negatively impacted the extending class's normal behavior. The code I was extending was open source so i ended up having to copy and paste the class and its dependencies into my project to do what I wanted. If I couldn't have done that then I'm not sure what the right approach would have been. 

In short, it is not always possible to know ahead of time how your clients will want to extend your API's functionality; artificially limiting this in my opinion will make it much harder to reuse components in previously unforeseen ways.

Kevin Lundberg

> On Dec 7, 2015, at 2:12 PM, Javier Soto via swift-evolution <swift-evolution at swift.org> wrote:
> This was brought up in a different thread about private by default. Creating a new thread for this. Quoting Mathew from the other thread with a short summary about the motivation behind this:
> "It is not uncommon to have a need for a reference type without a need for inheritance.  Superclasses should be intentionally designed to be subclasses and the author required to opt-in to subclassing and member overrides where that is required by the design."
> -- 
> Javier Soto 
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