Range<Int> substring finder for Swift Strings - Unsafe but Simple

String+IntRange.swift

//
//  String+IntRange.swift
//
//  Created by Zack Sheppard on 8/30/20.
//  Copyright © 2020 Zack Sheppard. All rights reserved.
//  Freely usable under the Apache 2.0 License.
//
import Foundation

/// This extension is freely available at
/// https://gist.github.com/zackdotcomputer/9d83f4d48af7127cd0bea427b4d6d61b
extension StringProtocol {
    /// Access the range of the search string as integer indices
    /// in the rendered string.
    /// - NOTE: This is "unsafe" because it may not return what you expect if
    ///     your string contains single symbols formed from multiple scalars.
    /// - Returns: A `Range<Int>` that will align with the Swift String.Index
    ///     from the result of the standard function range(of:).
    func rangeInt<S: StringProtocol>(of aString: S, options: String.CompareOptions = []) -> Range<Int>? {
        guard let range = range(of: aString, options: options) else { return nil }
        let start = distance(from: startIndex, to: range.lowerBound)
        return start..<start+distance(from: range.lowerBound, to: range.upperBound)  
    }
}