字符串：substringToIndex用于Unicode标量

Question

To get the first 50 characters of a String , I can do

s.substringToIndex(s.startIndex.advancedBy(50)))

How can I get the first 50 unicode scalars of a String ?

I can get a String.UnicodeScalarView object using s.unicodeScalars but I don't know how to go from there.

Answer 1

s.unicodeScalars returns a String.UnicodeScalarView which conforms to CollectionType . You can get a subsequence of the collection with

u = s.unicodeScalars
u[u.startIndex ..< u.startIndex.advancedBy(50)]

or, in the case of an initial sequence, more simply with

u.prefix(50)

There is a small difference: Subscripting requires that the specified subrange exists, and will terminate with a runtime exception otherwise. prefix() truncates at the given index, ie it returns a subsequence with 50 or less elements.