> If you need new values you just make new things. > If you want to do an operation on fooA, you don't mutate fooA. You call fooB = MyFunc(fooA) and use fooB.
The beautiful thing about this is you can stop naming things generically, and can start naming them specifically what they are. Comprehension goes through the roof.
Yes, but you can do that without having loads of stale copies of incorrect data lying around, presumably.