> On May 9, 2016, at 10:28 AM, Jacob Bandes-Storch via swift-users > <swift-users@swift.org> wrote: > > On Mon, May 9, 2016 at 10:25 AM, Joe Groff via swift-users > <swift-users@swift.org <mailto:swift-users@swift.org>> wrote: > > > On May 7, 2016, at 10:39 AM, Austin Zheng via swift-users > > <swift-users@swift.org <mailto:swift-users@swift.org>> wrote: > > > > Hello Swift users, > > > > I wanted to run something past you folks and get some opinions/feedback. > > > > About a month ago on Hacker News I saw someone commenting about how Swift's > > string-handling code was unbearably slow (3 seconds to run a code sample, > > vs. 0.8 in Java). I asked him to provide the code, and he obliged. > > Unfortunately, I didn't have time to dig into it until this morning. The > > code in its entirety can be found here: > > https://gist.github.com/austinzheng/d6c674780a58cb63832c4df3f809e683 > > <https://gist.github.com/austinzheng/d6c674780a58cb63832c4df3f809e683> > > > > At line 26 we have the following code: > > > > result.append(begin == eos ? "" : String(cs[begin..<end.successor()])) > > > > 'cs' is a UTF16 view into an input string, while 'result' is a [String]. > > When I profiled the code in Instruments, I noticed that it was spending > > significant time within the reflection machinery. > > > > It turns out that the initializer to make a String out of a utf16 view > > looks like this, and I believe this is the initializer the author intended > > to call: > > > > init?(_: String.UTF16View) > > > > However, the actual initializer being called was this String initializer in > > the Mirror code: > > > > public init<Subject>(_ instance: Subject) > > > > This seems like a tricky gotcha for developers who aren't extremely > > familiar with both the String and reflection APIs. His code looked > > reasonable at a first glance and I didn't suspect anything was wrong until > > I profiled it. Even so, I only made the connection because I recognized the > > name of the standard library function from poking around inside the source > > files. > > > > What do other people think? Is this something worth worrying about, or is > > it so rare that it shouldn't matter? Also, any suggestions as to how that > > code sample might be improved would be appreciated - my naive first attempt > > wasn't any better. > > This definitely strikes me as a problem. The String<T>(_:) constructor is > very easy to call by accident if you're trying to hit another unlabeled > initializer. It also strikes me as not particularly "value-preserving", since > stringifying many types loses information. Perhaps we should propose giving > it a label, String(printing:) maybe? > > +1
+1 - Daniel > > > -Joe > _______________________________________________ > swift-users mailing list > swift-users@swift.org <mailto:swift-users@swift.org> > https://lists.swift.org/mailman/listinfo/swift-users > <https://lists.swift.org/mailman/listinfo/swift-users> > > _______________________________________________ > swift-users mailing list > swift-users@swift.org > https://lists.swift.org/mailman/listinfo/swift-users
_______________________________________________ swift-users mailing list swift-users@swift.org https://lists.swift.org/mailman/listinfo/swift-users
