I’ll answer my own question (fired up xcode beta to try some stuff in swift 4):
>
> Is there a way of writing something looks like
>
> getLongergDeviceId()[<-2 from end> ... ]
>
> where whatever goes in the <-2 from the end> does NOT refer to
> getLongerDeviceID()?
and in swift 4, the answer is “yes.” If I simply overload the string subscript
operator to operate on CountablePartialRange<Int>, and I assume that positive
means offset from the beginning, and negative means relative to the end, then I
believe I can write something that is as efficient as one can get, using this
syntax:
let shortDeviceId = getLongerDeviceID[(-2)...]
let someOtherSlice = getLongerDeviceID[3...] // start at 3 from
beginning and go to end
So *I’ll* be happy. I just need to overload to handle all the different range
types. I’m sure there’s a reason for not including this in the API (i guess
there’s a need to be precise about what “units” one is talking about) but for
my purposes it gives an efficient and easy to read API.
I could imagine, just to avoid amiguity, perhaps
let someOtherSlice = getLongerDeviceID[UTF8.Index(3)...] //
start at 3 from beginning and go to end
which wouldn’t be the end of the world (compared with what we have now).
> I.e. I want to talk about -2 from the end as a concept without needing to
> refer to the specific string I’m talking about. If i could generate an index
> concept without referring to the string itself in anyway, i’d be happy. it’d
> be wonderful if i could express “-2 in whatever you feel like is the natural
> unit for the string you’re operating on.”
>
> Does the new API permit me to do that? If not, can I add my own subscript
> functions which take a new type, and i’ll invent the concept of “index in
> natural unit of the string being operated on.”
>
> thanks.
>
>
>
>
>
>
>>
>> On Sat, Jul 1, 2017 at 12:54 AM, David Baraff <[email protected]
>> <mailto:[email protected]>> wrote:
>>
>>> On Jun 30, 2017, at 9:48 PM, Taylor Swift via swift-users
>>> <[email protected] <mailto:[email protected]>> wrote:
>>>
>>>
>>> Swift's strings were very deliberately designed this way. It's tougher to
>>> get off the ground, sure, but it's better in the long run.
>>>
>>>
>>> It probably is, but the correct idiom is not very well known, and sadly
>>> most tutorials and unofficial guides are still teaching dumb ways of
>>> subscripting into strings (or worse, falling back into NSString methods
>>> without mentioning so) so the end result is people writing less performant
>>> code rather than more performant code.
>>
>> An efficient solution doesn’t help if even experienced programmers can’t
>> easily arrive at it. (I’m highly experienced, but I’ll admit I only put in
>> about 5 minutes before I posted that. on the other hand, it shouldn’t take
>> 5 minutes to figure out something that simple with strings. still, maybe i
>> would have done the simple “suffix()” thing had i been looking at the actual
>> swift 4 api’s, but i only had swift 3 api’s in front of me.)
>>
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>>
>>
>
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