A set of lazy(!) extensions for String to allow index-based indexing

String+LazyIndexExtensions.swift

//
//  String+extensions.swift
//
//  Created by Darren Ford on 6/4/20.
//
//  Lazy extensions for Swift Strings indexing
//
//  For example :-
//   let value = "Caterpillar"
//   let catStr = value.substring(0 ..< 3)

import Foundation

extension String {
   func substring(_ range: Range<Int>) -> String {
      return String(self[self.range(range)])
   }

   func substring(_ range: PartialRangeFrom<Int>) -> String {
      return String(self[self.range(range)])
   }

   func substring(_ range: PartialRangeUpTo<Int>) -> String {
      return String(self[self.range(range)])
   }

   func substring(_ range: PartialRangeThrough<Int>) -> String {
      return String(self[self.range(range)])
   }

   func range(_ range: Range<Int>) -> Range<String.Index> {
      let si = self.index(self.startIndex, offsetBy: range.lowerBound)
      let ei = self.index(self.startIndex, offsetBy: range.upperBound)
      return si ..< ei
   }

   func range(_ range: ClosedRange<Int>) -> ClosedRange<String.Index> {
      let si = self.index(self.startIndex, offsetBy: range.lowerBound)
      let ei = self.index(self.startIndex, offsetBy: range.upperBound)
      return si ... ei
   }

   func range(_ partialRange: PartialRangeFrom<Int>) -> Range<String.Index> {
      let si = self.index(self.startIndex, offsetBy: partialRange.lowerBound)
      return si ..< self.endIndex
   }

   func range(_ partialRange: PartialRangeThrough<Int>) -> Range<String.Index> {
      let ei = self.index(self.startIndex, offsetBy: partialRange.upperBound + 1)
      return self.startIndex ..< ei
   }

   func range(_ partialRange: PartialRangeUpTo<Int>) -> Range<String.Index> {
      let ei = self.index(self.startIndex, offsetBy: partialRange.upperBound)
      return self.startIndex ..< ei
   }
}