Add subscript(r: Range<Int>) to String

Originator:robnapier
Number:rdar://17158813 Date Originated:04-Jun-2014
Status:Open Resolved:
Product:Swift Product Version:
Classification: Reproducible:
 
You should be able to slice strings by integers rather than hard-to-create StringIndexes. Here is a simple implementation:

import Foundation

extension String {
  subscript (r: Range<Int>) -> String { 
    get {
        return self.substringWithRange(
          Range(start: advance(self.startIndex, r.startIndex),
            end: advance(self.startIndex, r.endIndex)))
    }
  }
}

var s = "Hello, playground"

println(s[0 .. 5])

==> Hello

Comments

ellpisis .. ...

oops! When I suggested this "correction" above, I was not aware of the different range specifiers with .. (two dots) or ... (three dots) so, the "start + 1 is unnecessary.. Sorry.

By tedvga at June 7, 2014, 8:17 a.m. (reply...)

suggestion for further improvement s[n] and s[n1..n2] and use of existing functions concatenated

extension String { 

// single subscript s[n]


subscript (idx: Int) -> String
{
    get
    {
        return self.substringWithRange(
            Range( start: advance( self.startIndex, idx),
                end: advance( self.startIndex, idx + 1 )  )
        )
    }
}

// range subscript [n1..n2]
// end index corrected: added one so that
// e.g  "abcdefgh"[2..4] gives "cde" not "cdef" ..

subscript (r: Range<Int>) -> String
    {
    get
    {
        return self.substringWithRange(
            Range( start: advance( self.startIndex, r.startIndex),
                end: advance( self.startIndex, r.endIndex + 1 ))              )
    }
}

// N.B. there is no proper invalid range detection/assert in substringWitRange!
// it returns "characters" from memory exceeding the strings allocation!
//

// using existing functions concatenated

func substringFrom(start: Int, to: Int) -> String
{
    return (self.substringFromIndex(start)).substringToIndex(to - start + 1)
}

}

Evaluated in the XCode playground:

var s = "abcdefghijklmnopqrstuvwxyz"

var sub2 = s[4..12] //"efghijklm"

var c = s[5] // "f"

"abcdefgh"[2..4] // "cde"

let s2 = s.substringFrom(5, to: 24) // "fghijklmnopqrstuvwxy"

Kind Regards

Ted

By tedvga at June 5, 2014, 3:24 p.m. (reply...)

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