> On Jun 10, 2017, at 19:01, Charles Srstka via swift-evolution 
> <swift-evolution@swift.org> wrote:
> 
>> On Jun 8, 2017, at 2:35 PM, Tony Allevato via swift-evolution 
>> <swift-evolution@swift.org> wrote:
>> 
>> It is an extremely rare case for a developer to know a priori what literal 
>> numeric indices should be used when indexing into a string, because it only 
>> applies when strings fall into a very specific format and encoding.
> 
> Knowing this is required for accessibility support on macOS, since it’s 
> needed to implement NSAccessibility methods such as 
> accessibilityAttributedString(for:), accessibilityRTF(for:), 
> accessibilityFrame(for:), etc.

I think Tony was getting at knowing the best indices for a string, vs. a format 
or API that is documented to use UTF-8 or UTF-16 indexes specifically (like, 
unfortunately, most of Cocoa and Cocoa Touch). It stinks that those may not be 
random-access if the underlying string buffer turns out to not be UTF-16, but 
that's true with NSString as well.

Jordan

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