[swift-dev] State of String: ABI & Performance

[Michael Ilseman]

> On Jan 11, 2018, at 4:20 PM, Ben Cohen <ben_cohen at apple.com> wrote:
> 
> 
> 
>> On Jan 11, 2018, at 12:32 PM, Michael Ilseman via swift-dev <swift-dev at swift.org <mailto:swift-dev at swift.org>> wrote:
>> 
>> For a more general solution, I think a `var numericValue: Int? { get }` on Character would make sense. Unicode defines (at least one) semantics for this and ICU provides this functionality already.
>> 
> 
> Minor style point – this should be a failable init on Int rather than a computed property on Character
> 
> i.e. Int.init?(_: Character), matching Int.init?(_: String, radix: Int = 10), only it doesn’t need the radix arg cos it’s only a single character.
> 

`Int.init?` is probably better, yes. If you wanted to take that to its logical conclusion, that would include `Double.init?` for mathematical constants and some `Rational.init` for fraction graphemes. These are pretty far off the deep end ;-)

Minor logic point – radix isn't important, but that's not because it’s only a single character but rather because of how Unicode(/ICU) defines character properties. Numbers can be much higher than 9, e.g. 万 is ten-thousand. Even worse is cuneiform, which is sexagesimal (and of course cuneiform is properly encoded in Unicode!). Luckily, Unicode’s numeric values are always presented in base-10, AFAICT.


> If implemented inside the std lib, it can still access character’s internals, which is a reasonable thing to do for something so performance-sensitive.
> 

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