but I believe it would be better to let the (D) compiler
optimization stage figure out _automatically_ if it needs to
make a copy of the variable `numbers` or not depending on
whether `numbers` is used or not further down the body of
`main`.
I just realized that solving this in an elegant way (for
reference types) would require some kind of new builtin property,
say,
r.isUnique
The compiler could, when possible, do this check at compile-time,
and avoid any run-time (GC) or reference counting overheads done
in isUnique.
I just found that this is highly related:
http://wiki.dlang.org/DIP29
