[swift-evolution] [Idea] Add forced conversion for Error catching pattern matching

[Radosław Pietruszewski]

> Also as a brief aside, it’s not super intuitive to me that the syntax for the catch pattern matching wildcard is 
> 
> catch _
> 
> whereas it is
> 
> default
>  
> for switches.

I do believe you can just say `catch`:

  4> do {
  5.     try throwing()
  6. } catch let e as E { ...
  7. } catch {
  8.     print(error)
  9. }

— Radek

> On 20 Mar 2016, at 21:26, Tyler Fleming Cloutier via swift-evolution <swift-evolution at swift.org> wrote:
> 
> I recall that there was quite a bit of discussion a while back about adding typed error declarations for methods that throw for the purpose of exhaustive pattern matching on errors.
> 
> There were interesting arguments on either side, and I think that the result was to maintain the status quo. There’s still the issue of having to add the extra catch statement to every do block for exhaustive matches.
> 
> Would it be wise to allow force conversion for the cases in which the developer believes the match is exhaustive? ie
> 
> do {
>     let action = chooseAction(game)
>     game = try game.applyAction(action)
> } catch let e as ActionError {
>     game.failedAction = e
> } catch _ {
>     fatalError(“This is an unfortunate bit of noise :/")
> }
> 
> becomes
> 
> do {
>     let action = chooseAction(game)
>     game = try game.applyAction(action)
> } catch let e as! ActionError {
>     game.failedAction = e
> }
> 
> 
> Also as a brief aside, it’s not super intuitive to me that the syntax for the catch pattern matching wildcard is 
> 
> catch _
> 
> whereas it is
> 
> default
>  
> for switches. I think I saw Chris mention somewhere that default was chosen because of it’s wide familiarity. Does anyone recall the reason?
> 
> Thanks,
> 
> Tyler
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