Is SubString a necessary type?

[sveinhal (Svein Halvor Halvorsen)]

Java has a lot of experience in this department. So much so, that they decided to replace the implementation of .substring():

Cannot assign value of type 'String' to subscript of type 'String.SubSequence'

I think Java used to (until around 2012 or thereabouts) implement String like our Substring type. That is, a string would hold a character buffer combined with an offset and a length. Calling .substring on a string would return a String type (but again, similar to our Substring) with the same buffer, but a different length and offset. They changed that because the overwhelming number of string manipulations weren't parsers, scanners and other cases where that optimisation mattered. Their Strin…