AttributedString to String

Using Swift
2

As far as I can tell, there are currently two ways to fetch a String from an AttributedString at the moment, both revolving around AttributedString.CharacterView:

  1. String has an initializer which takes a Sequence of Characters and constructs itself from that sequence. Given an AttributedString attrStr, you can write String(attrStr.characters).

    However: I believe there's may be a performance pitfall here, because as far as I can tell, there's currently no fast-path in place here to help avoid iterating over characters one character at a time with a regular for-in loop, which is slower than getting to copy bytes from an underlying buffer directly

  2. It's not particularly intuitive to find, but the AttributedString work added an initializer to String which takes a slice of an AttributedString, reaches into its _guts to grab the underlying String, slices the underlying String, and returns a bulk copy of that.

    Although also necessarily an O(n) copy, ths should be faster in practice than iterating over the character view and copying one character at a time.

    You can achieve this at the moment by writing String(attrStr.characters[...]).

I haven't thought through the slicing aspects, but it appears to me that not offering read access to the underlying String directly may only be an API oversight. Someone from the Foundation team, feel free to correct me, but this may be worth filing Feedback for. (As an alternative, it also seems reasonable to offer String.init(_: AttributedString.CharacterView) and String.init<S: AttributedStringProtocol>(_: S) as fast-path shortcuts for performing this conversion with fewer performance implications.)

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