[swift-evolution] Followup after in-the-field feedback for SE-0170

[Jordan Rose]

> On Jun 14, 2017, at 13:59, Philippe Hausler via swift-evolution <swift-evolution at swift.org> wrote:
> 
> 
> 
>> On Jun 14, 2017, at 1:47 PM, Dave Abrahams via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>> 
>> on Wed Jun 14 2017, Philippe Hausler <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> 
>>> After implementing the proposal
>>> https://github.com/apple/swift-evolution/blob/master/proposals/0170-nsnumber_bridge.md <https://github.com/apple/swift-evolution/blob/master/proposals/0170-nsnumber_bridge.md>
>>> <https://github.com/apple/swift-evolution/blob/master/proposals/0170-nsnumber_bridge.md <https://github.com/apple/swift-evolution/blob/master/proposals/0170-nsnumber_bridge.md>>
>>> we have gotten some initial feedback.
>>> 
>>> It seems that there is definitely a fair amount of confusion and heartache for dealing with Float
>>> and Double values being bridged.
>>> 
>>> Specifically the cases like:
>>> 
>>> NSNumber(value 0.1) as? Float
>>> 
>>> which with the current implementation will return nil since the Double value 0.1 cannot be
>>> represented exactly as a Float.
>>> 
>>> It seems like the overwhelming majority of users know full well that
>>> Float will result in a loss of precision (hence why they chose that
>>> type over Double). This means that the floating point bridges for
>>> Double, Float, and CGFloat should not be the pedantic “exactly” cases
>>> but instead infer the conversion intent of a lax/approximated version.
>> 
>> +1
>> 
>>> So in short: for the betterment of the API ergonomics, the floating
>>> point types as destinations will be pulled back to their initial Swift
>>> 3 behavior.
>>> 
>>> Additionally to aide appropriate migration to the appropriate
>>> truncating/exactly initializers the un-labeled, deprecated in Swift 4,
>>> plain init methods to the numeric types with an NSNumber will now be
>>> annotated with the suggested replacements.
>> 
>> Sorry, I don't quite understand what that last paragraph implies.  Could
>> you describe what will be deprecated and what will be suggested instead?
> 
> https://github.com/phausler/swift/commit/62218c85b6c494c4054ec9774dd6ce095a5d0fa4 <https://github.com/phausler/swift/commit/62218c85b6c494c4054ec9774dd6ce095a5d0fa4>
> 
> So this is just an annotation of renaming to the init(truncating:)

How about cases where the value is a double that's greater than Float.greatestFiniteMagnitude? Should/Will that produce 'nil' or Float.infinity?

Jordan

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