string replace substring without NSString API - swift

Question

I would like to be able to find and replace occurrences of a substring in a native Swift string without bridging to the NS class. How can I accomplish this?
This is not a duplicate of this question, as that question is about replacing a single character. This question is about finding and replacing a substring, which may contain many characters.

Answer 1

Method without Foundation:
extension String {
func replacing(_ oldString: String, with newString: String) -> String {
guard !oldString.isEmpty, !newString.isEmpty else { return self }
let charArray = Array(self.characters)
let oldCharArray = Array(oldString.characters)
let newCharArray = Array(newString.characters)
var matchedChars = 0
var resultCharArray = [Character]()
for char in charArray {
if char == oldCharArray[matchedChars] {
matchedChars += 1
if matchedChars == oldCharArray.count {
resultCharArray.append(contentsOf: newCharArray)
matchedChars = 0
}
} else {
for i in 0 ..< matchedChars {
resultCharArray.append(oldCharArray[i])
}
if char == oldCharArray[0] {
matchedChars = 1
} else {
matchedChars = 0
resultCharArray.append(char)
}
}
}
return String(resultCharArray)
}
}
Example usage:
let myString = "Hello World HelHelloello Hello HellHellooo"
print(myString.replacing("Hello", with: "Hi"))
Output:
Hi World HelHiello Hi HellHioo
Method using Foundation:
You can use the replacingOccurrences method on the String struct.
let myString = "Hello World"
let newString = myString.replacingOccurrences(of: "World", with: "Everyone")
print(newString) // prints "Hello Everyone"

Answer 2

generic and pure Swift approach
func splitBy<T: RangeReplaceableCollection>(_ s:T, by:T)->[T] where T.Iterator.Element:Equatable {
var tmp = T()
var res = [T]()
var i:T.IndexDistance = 0
let count = by.count
var pc:T.Iterator.Element {
get {
i %= count
let idx = by.index(by.startIndex, offsetBy: i)
return by[idx]
}
}
for sc in s {
if sc != pc {
i = 0
if sc != pc {
} else {
i = i.advanced(by: 1)
}
} else {
i = i.advanced(by: 1)
}
tmp.append(sc)
if i == count {
tmp.removeSubrange(tmp.index(tmp.endIndex, offsetBy: -i)..<tmp.endIndex)
res.append(tmp)
tmp.removeAll()
}
}
res.append(tmp)
return res
}
func split(_ s:String, by:String)->[String] {
return splitBy(s.characters, by: by.characters).map(String.init)
}
extension RangeReplaceableCollection where Self.Iterator.Element: Equatable {
func split(by : Self)->[Self] {
return splitBy(self, by: by)
}
}
how to use it?
let str = "simple text where i would like to replace something with anything"
let pat = "something"
let rep = "anything"
let s0 = str.characters.split(by: pat.characters).map(String.init)
let res = s0.joined(separator: rep)
print(res) // simple text where i would like to replace anything with anything
let res2 = split(str, by: pat).joined(separator: rep)
print(res2) // simple text where i would like to replace anything with anything
let arr = [1,2,3,4,1,2,3,4,1,2,3]
let p = [4,1]
print(arr.split(by: p)) // [[1, 2, 3], [2, 3], [2, 3]]