let firstLetter = myString.characters.first lør. 18. jun. 2016 kl. 04.38 skrev Brent Royal-Gordon via swift-users < swift-users@swift.org>:
> > I've previously used myString[0...1] to get the first character of a > string. > > I'm not sure how, because this has never worked in Swift. Strings use > opaque indices which specifically prevent you from doing this, so you have > never been able to subscript a string with integers or ranges of integers. > It's done this way because indexing into a Unicode string intrinsically > requires walking through the data structure and counting characters one at > a time; the lack of integer indices is meant to force you to explicitly > write `index(after:)` or `index(_:offsetBy:)` (formerly `successor()` or > `advancedBy(_:)`) in your code to make this cost obvious. > > > What documentation is this referring to? There's no right-click > definition available, nothing in Navigator, and Google fails to turn up > anything. > > The standard library includes definitions of these subscripts which are > meant to direct you to documentation explaining why they're not supported, > but these definitions don't show up in the generated interfaces. Presumably > Xcode is removing all APIs marked "unavailable". The doc comment it's > trying to direct you to is here < > https://github.com/apple/swift/blob/b8401e1fde52d95e5a8ce7b043a3c5a3bcf72181/stdlib/public/core/UnavailableStringAPIs.swift.gyb#L15 > >: > > /// Subscripting strings with integers is not available. > /// > /// The concept of "the `i`th character in a string" has > /// different interpretations in different libraries and system > /// components. The correct interpretation should be selected > /// according to the use case and the APIs involved, so `String` > /// cannot be subscripted with an integer. > /// > /// Swift provides several different ways to access the character > /// data stored inside strings. > /// > /// - `String.utf8` is a collection of UTF-8 code units in the > /// string. Use this API when converting the string to UTF-8. > /// Most POSIX APIs process strings in terms of UTF-8 code units. > /// > /// - `String.utf16` is a collection of UTF-16 code units in > /// string. Most Cocoa and Cocoa touch APIs process strings in > /// terms of UTF-16 code units. For example, instances of > /// `NSRange` used with `NSAttributedString` and > /// `NSRegularExpression` store substring offsets and lengths in > /// terms of UTF-16 code units. > /// > /// - `String.unicodeScalars` is a collection of Unicode scalars. > /// Use this API when you are performing low-level manipulation > /// of character data. > /// > /// - `String.characters` is a collection of extended grapheme > /// clusters, which are an approximation of user-perceived > /// characters. > /// > /// Note that when processing strings that contain human-readable > /// text, character-by-character processing should be avoided to > /// the largest extent possible. Use high-level locale-sensitive > /// Unicode algorithms instead, for example, > /// `String.localizedStandardCompare()`, > /// `String.localizedLowercaseString`, > /// `String.localizedStandardRangeOfString()` etc. > > > -- > Brent Royal-Gordon > Architechies > > _______________________________________________ > swift-users mailing list > swift-users@swift.org > https://lists.swift.org/mailman/listinfo/swift-users >
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