What is a slice in Swift?

Question

What is a slice in Swift and how does it differ from an array?

From the documentation, the type signature of subscript(Range) is:

subscript(Range<         


        

Answer 1

Summary:

The answers above were true up until Beta 3 (and may change again in future releases)

Slice now acts just like an array, but as @matt said above, is effectively a shallow copy to an array under the hood, until a change is made. Slices (now) see a snapshot of the original values,

Also note that slice syntax has changed:

[from..upToButNotIncluding] -> [from..

Example:

var arr = ["hello", "world", "goodbye"] // ["hello", "world", "goodbye"]
var arrCopy = arr
let slice = arr[0..<2]                  // ["hello", "world"]
arr[0] = "bonjour"
arr                                     // ["bonjour", "world", "goodbye"]
arrCopy                                 // ["hello", "world", "goodbye"]
slice                                   // ["hello", "world"]

This allows much more uniform processing, as it is simpler (IMHO) to do python style list processing - filtering one list to make another. per Matt's answer prior to Beta 3, you had to create a temporary array in order to map a slice. The new code is now simpler:

class NameNumber {
    var name:String = ""
    var number:Int = 0

    init (name:String, number:Int) {
        self.name = name
        self.number = number
    }
}

var number = 1
let names = ["Alan", "Bob", "Cory", "David"]
let foo = names[0..<2].map { n in NameNumber(name:n, number:number++) }
foo     // [{name "Alan" number 1}, {name "Bob" number 2}]

(though to be fair, foo is still a slice)

Reference:

http://adcdownload.apple.com//Developer_Tools/xcode_6_beta_3_lpw27r/xcode_6_beta_3_release_notes__.pdf

Important Changes, Issues Resolved, - Swift Language, Paragraph 1

"Array in Swift has been completely redesigned to have full value semantics like Dictionary and String...m"