>> Does this really count as mutability though? Not really. The string would be thrown away anyway so this is just an optimization to reuse the memory. The important takeaway here is that you are not allocating a new string every single time like the internet says.
The important takeaway is that semantic immutability does not require or depend on implementation immutability. It's a 'levels of abstraction' thing. Once you let the users peek behind the curtain, however, it becomes much more difficult to be sure they cannot shoot themselves in the foot by so doing.
The important takeaway is that semantic immutability does not require or depend on implementation immutability. It's a 'levels of abstraction' thing. Once you let the users peek behind the curtain, however, it becomes much more difficult to be sure they cannot shoot themselves in the foot by so doing.