[swift-evolution] [swift-evolution-announce] [Review] SE-0117: Default classes to be non-subclassable publicly

[Scott James Remnant]

> On Jul 6, 2016, at 2:13 PM, Leonardo Pessoa <me at lmpessoa.com> wrote:
> 
> You can also try and simplify your outlines reducing X.c and X.d to a
> single entry as it is the same rule applied to two different elements
> of the language. Using one single keyword (such as in 'open') would
> make it clearer and that is why I prefer to have only one keyword.
> 

I didn’t simply the outlines precisely because the proposal suggests two keywords.

One keyword does solve this problem, but not the problem of conflation of finality and access control.
You end up with this matrix:

  access      | can override | final
 -------------+--------------+-------
  open        | yes          | Error - “class cannot be open and final"
  public      | no           | Error - “public class is already final by default"
  internal    | yes          | final
  fileprivate | yes          | final
  private     | yes          | final

This is way more confusing than the current language:

  access      | can override | final
 -------------+--------------+-------
  public      | yes          | final
  internal    | yes          | final
  fileprivate | yes          | final
  private     | yes          | final

I strongly favor a programming language that doesn’t introduce compiler errors to solve problems that could be solved by cleaner syntax.

Since it’s already necessary to place the `public` keyword in front of every class, method, property, or subscript that you intend to make public, the developer is already thinking about the public API. Typing `public final` instead of `public` is an extra keyword, it’s not an extra cognitive burden since that cognition is already taking place.

Scott

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