> On Apr 18, 2017, at 12:17 PM, Joe Groff <[email protected]> wrote:
>
>
>> On Apr 17, 2017, at 5:56 PM, Xiaodi Wu via swift-evolution
>> <[email protected]> wrote:
>>
>> It seems Float.init(exactly: NSNumber) has not been updated to behave
>> similarly?
>>
>> I would have to say, I would naively expect "exactly" to behave exactly as
>> it says, exactly. I don't think it should be a synonym for
>> Float(Double(exactly:)).
>> On Mon, Apr 17, 2017 at 19:24 Philippe Hausler via swift-evolution
>> <[email protected]> wrote:
>> I posted my branch and fixed up the Double case to account for your concerns
>> (with a few inspired unit tests to validate)
>>
>> https://github.com/phausler/swift/tree/safe_nsnumber
>>
>> There is a builtin assumption here though: it does presume that the swift’s
>> representation of Double and Float are IEEE compliant. However that is a
>> fairly reasonable assumption in the tests.
>
> (+Steve Canon) What is the behavior of Float.init(exactly: Double)?
> NSNumber's behavior would ideally be consistent with that.
The implementation is essentially just:
self.init(other)
guard Double(self) == other else {
return nil
}
i.e. if the result is not equal to the source when round-tripped back to double
(which is always exact), the result is nil.
– Steve
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