[swift-dev] String comparison improvements

Itai Ferber iferber at apple.com
Wed Jan 17 15:46:44 CST 2018

Hi Lance,

I read Michael’s emails but I don’t remember at the moment — what 
is the new string comparison implementation going to be based on?
Also, how will this affect bridged strings? If I compare two 
`NSString`s, I may get a different result than if I compare the same two 
strings as bridged through `String`, correct?

— Itai

On 17 Jan 2018, at 13:19, Lance Parker via swift-dev wrote:

> Hey Swift-Dev,
> The swift standard library team  have been working on a new 
> implementation for comparing Swift strings for Swift 5. Michael 
> touched on the motivations in the State of String email but I’ll 
> summarize here:
> The Swift String comparison implementations on Apple platforms and 
> Linux differ in results and performance. Apple platforms use 
> CFStringCompare with no locale, while Linux uses ICU libraries. 
> Unifying the algorithms that Swift strings use for comparison is 
> reason alone for doing a new implementation.
> We've come up with some great common fast paths that speed up 
> comparisons for a lot of common cases. Our microbenchmarks show up to 
> a 6.8x increase in performance and there is still some low hanging 
> fruit in our implementation that would bring further speedups.
> Bare in mind this is not intended to be a replacement for sorting 
> strings that will be presented to users, for that developers should 
> stick to NSLocalizedString APIs.

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