error[E0382]: use of moved value: `x`
  --> $DIR/moves-based-on-type-tuple.rs:4:18
   |
LL | fn dup(x: Box<isize>) -> Box<(Box<isize>,Box<isize>)> {
   |        - move occurs because `x` has type `Box<isize>`, which does not implement the `Copy` trait
...
LL |     Box::new((x, x))
   |               -  ^ value used here after move
   |               |
   |               value moved here
   |
help: consider cloning the value if the performance cost is acceptable
   |
LL |     Box::new((x.clone(), x))
   |                ++++++++

error: aborting due to previous error

For more information about this error, try `rustc --explain E0382`.
