[S32/Temporal] Reverted DateTime back to being mutable. I think we ought to
make a big change like this only after reaching some kind of consensus to do
so, not least because I just implemented a lot of mutating methods!
Note that += and friends need only the *container* on the LHS to be mutable,
not the value?\226?\128?\148'$x += 1' should be allowed whether $x holds an
Int, a Date, or a DateTime.
Types representing temporal artifacts should *not* be mutable; they should be
If you want to derive a DateTime from another, say, then just have the
pseudo-mutator method return a new object with the differences.
-- Darren Duncan