[swift-evolution] [Proposal] Type Narrowing

[Jean-Daniel]

> Le 7 nov. 2016 à 04:52, Chris Lattner via swift-evolution <swift-evolution at swift.org> a écrit :
> 
> 
>> On Nov 3, 2016, at 10:04 AM, Haravikk via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>> To avoid hijacking the guard let x = x thread entirely I've decided to try to write up a proposal on type narrowing in Swift.
>> Please give your feedback on the functionality proposed, as well as the clarity of the proposal/examples themselves; I've tried to keep it straightforward, but I do tend towards being overly verbose, I've always tried to have the examples build upon one another to show how it all stacks up.
> 
> FWIW, we have specifically considered something like this proposal in the past.  You didn’t mention it, but the ?: operator is a specific example that frequently comes up.  People often expect to be able to do something like:
> 
> 	… = foo is B ? foo.bMethod() : …
> 

For the case of the ?: operator, I think it can be replaced by a ?? operator for most cases:

… = (foo as B)?.bMethod() ?? …