[swift-evolution] Pitch: Member lookup on String should not find members of NSString

[Ted Kremenek]

A complementary tactic would be that migration tool support to Swift 5 would insert the needed casts to NSString.  That way even if the magic lookup is gone in Swift 5 the code could be automatically migrated and preserve the same semantics.  If this came to a formal proposal I’d really like to see something like that considered.

> On Oct 24, 2017, at 3:56 PM, Slava Pestov via swift-evolution <swift-evolution at swift.org> wrote:
> 
> I think to maintain source compatibility, the old behavior would be preserved until/if we remove -swift-version 4 mode. By deprecating it though, we won’t have to devote as much time to maintaining it going forward.
> 
> Slava
> 
>> On Oct 24, 2017, at 3:54 PM, Philippe Hausler <phausler at apple.com> wrote:
>> 
>> I think any serious proposal with the removal of APIs would need to consider source compatibility and to do so you should likely audit the API surface area that is being offered (and replace it via the NSStringAPI.swift extension)
>> 
>>> On Oct 24, 2017, at 3:12 PM, Slava Pestov via swift-evolution <swift-evolution at swift.org> wrote:
>>> 
>>> Perhaps you could write up a proposal to outline the missing functionality :-)
>>> 
>>> Slava
>>> 
>>>> On Oct 24, 2017, at 3:09 PM, Jonathan Hull <jhull at gbis.com> wrote:
>>>> 
>>>> I would feel better about it if String gained a lot of the utility of NSString (so that we don’t have to go to NSString all the time for methods)
>>>> 
>>>> Thanks,
>>>> Jon
>>>> 
>>>>> On Oct 24, 2017, at 3:00 PM, Slava Pestov via swift-evolution <swift-evolution at swift.org> wrote:
>>>>> 
>>>>> Hi,
>>>>> 
>>>>> Members of NSString, except those defined in Foundation, are available on values of type String. For example,
>>>>> 
>>>>> extension NSString {
>>>>> @objc func foo() {}
>>>>> }
>>>>> 
>>>>> let s: String = “hello”
>>>>> 
>>>>> s.foo()
>>>>> 
>>>>> We don’t do this for any other bridged types, for instance NSArray methods are not imported as Array methods. It’s literally a special case in the type checker for member lookup on String.
>>>>> 
>>>>> This behavior doesn’t really much sense conceptually and it was put in as a stop-gap in Swift 1 to beef up the String API. I would like to phase it out as follows:
>>>>> 
>>>>> - Unconditional warning in Swift 4.1, with a fixit to insert an ‘as NSString’ cast
>>>>> - Error in Swift 5 with -swift-version 5
>>>>> 
>>>>> What does everyone think about this?
>>>>> 
>>>>> Slava
>>>>> _______________________________________________
>>>>> swift-evolution mailing list
>>>>> swift-evolution at swift.org
>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>> 
>>> 
>>> _______________________________________________
>>> swift-evolution mailing list
>>> swift-evolution at swift.org
>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>> 
> 
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution