[swift-evolution] Proposal: Do not allow redundant unwrapping.

[Amir Michail]

> On Dec 9, 2015, at 12:13 PM, Joe Groff <jgroff at apple.com> wrote:
> 
> 
>> On Dec 9, 2015, at 6:31 AM, Amir Michail via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>> The following should result in a compile error:
>> 
>> var x:Int? = 5
>> var y:Int?
>> 
>> y = x! // compiler error, unwrapping is redundant
>> 
>> The unnecessary unwrapping gives the wrong impression about the type of y — namely that it is Int.
> 
> The compiler doesn't know this. You gave x type 'Int?', not 'Int’.

It knows this because x! has type Int and y has type Int?. So the unwrapping is unnecessary prior to the assignment to y. You should have just written “y = x”.

> 
> -Joe
> 
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