If strings are immutable in .NET, then why does Substring take O(n) time?

Question

Given that strings are immutable in .NET, I\'m wondering why they have been designed such that string.Substring() takes O(substring.Length) time, i

Answer 1

Java (as opposed to .NET) provides two ways of doing Substring(), you can consider whether you want to keep just a reference or copy a whole substring to a new memory location.

The simple .substring(...) shares the internally used char array with the original String object, which you then with new String(...) can copy to a new array, if needed (to avoid hindering garbage collection of the original one).

I think this kind of flexibility is a best option for a developer.