For a class/interface type `A` and a class `C` inheriting from
`A` one can do
A a = getA();
if (auto c = cast(C) a)
{ .. use c .. }
to get a `C` view on `a` if it happens to be a `C`-instance.
Sometimes one cannot find a good new name for `c` while there is
no advantage of accessing `a` when `c` is available. D does not
allow to shadow `a` in the if-auto declaration for good reasons.
How about relaxing the rule for cases like these, where the rhs
is the lhs with a cast to derived?
if (auto a = cast(C) a)
{ .. use a typed as C .. }
One can think of `a` being *statically* retyped to `C` as this is
a (strictly) better type information. Internally, it would be a
shadowing, but it does not matter as the disadvantages don't
apply (if I didn't miss something).
