Range<String.Index> Versus String.Index

Question

I am having an issue understanding the difference between Range-String.Index- and String.Index

For example:

func returnHtmlContent() -> String {
    let filePath = URL(string:"xxx.htm")
    filePath?.startAccessingSecurityScopedResource();
    let htmlFile = Bundle.main.path(forResource: "getData", ofType: "htm");
    let html = try! String(contentsOfFile: htmlFile!, encoding: String.Encoding.utf8);
    filePath?.stopAccessingSecurityScopedResource();
    return html;
};
func refactorHtml(content: String) -> String {
    let StartingString = "<div id=\"1\">";
    let EndingString   = "</div></form>";

    func selectString() -> String {
        var htmlContent = returnHtmlContent();
        let charLocationStart = htmlContent.range(of: StartingString);
        let charLocationEnd   = htmlContent.range(of: EndingString);

        htmlContent.remove(at: charLocationStart);
        return htmlContent;
    };
    let formattedBody = selectString();
    return formattedBody;
};
refactorHtml(content: returnHtmlContent());

The idea in pseudocode

Generated HTMLBody
Pass To Function that formats
Remove all characters before StartingString
Remove all Characters After EndingString
Send NewString to Variable

Now - when I try to find the index position I cant seem to get the right value type, this is the error I am getting

Cannot convert value of type 'Range<String.Index>?' to expected argument type 'String.Index'

This is running in a playground

Answer 1

String indices aren't integers. They're opaque objects (of type String.Index ) which can be used to subscript into a String to obtain a character.

Ranges aren't limited to only Range<Int> . If you look at the declaration of Range , you can see it's generic over any Bound , so long as the Bound is Comparable (which String.Index is).

So a Range<String.Index> is just that. It's a range of string indices, and just like any other range, it has a lowerBound , and an upperBound .