How to get all strings between particular delimiters? - ios

Question

I have a string called source. This string contains tags, marked with number signs (#) on left and right side.
What is the most efficient way to get tag names from the source string.
Source string:
let source = "Here is tag 1: ##TAG_1##, tag 2: ##TAG_2##."
Expected result:
["TAG_1", "TAG_2"]

Answer 1

Not a very short solution, but here you go:
let tags = source.componentsSeparatedByCharactersInSet(NSCharacterSet(charactersInString: " ,."))
.filter { (str) -> Bool in
return str.hasSuffix("##") && str.hasPrefix("##")
}
.map { (str) -> String in
return str.stringByReplacingOccurrencesOfString("##", withString: "")
}

Answer 2

Split the string at all occurences of ##:
let components = source.components(separatedBy: "##")
// Result: ["Here is tag 1: ", "TAG_1", ", tag 2: ", "TAG_2", "."]
Check that there's an odd number of components, otherwise there's an odd amount of ##s:
guard components.count % 2 == 1 else { fatalError("Unbalanced delimiters") }
Get every second element:
components.enumerated().filter{ $0.offset % 2 == 1 }.map{ $0.element }
In a single function:
import Foundation
func getTags(source: String, delimiter: String = "##") -> [String] {
let components = source.components(separatedBy: delimiter)
guard components.count % 2 == 1 else { fatalError("Unbalanced delimiters") }
return components.enumerated().filter{ $0.offset % 2 == 1 }.map{ $0.element }
}
getTags(source: "Here is tag 1: ##TAG_1##, tag 2: ##TAG_2##.") // ["TAG_1", "TAG_2"]

Answer 3

You can read this post and adapt the answer for your needs: Swift: Split a String into an array
If not you can also create your own method, remember a string is an array of characters, so you can use a loop to iterate through and check for a '#'
let strLength = source.characters.count;
var strEmpty = "";
for( var i=0; i < strLength; i++ )
{
if( source[ i ] == '#' )
{
var j=(i+2);
for( j; source[ (i+j) ] != '#'; j++ )
strEmpty += source[ (i+j) ]; // concatenate the characters to another variable using the += operator
i = j+2;
// do what you need to with the tag
}
}
I am more of a C++ programmer than a Swift programmer, so this is how I would approach it if I didn't want to use standard methods. There may be a better way of doing it, but I don't have any Swift knowledge.
Keep in mind if this does not compile then you may have to adapt the code slightly as I do not have a development environment I can test this in before posting.