error[E0229]: associated item constraints are not allowed here
  --> $DIR/no-gat-position.rs:6:56
   |
LL |     fn next<'a>(&'a mut self) -> Option<Self::Item<'a, As1: Copy>>;
   |                                                        ^^^^^^^^^ associated item constraint not allowed here
   |
help: consider removing this associated item constraint
   |
LL -     fn next<'a>(&'a mut self) -> Option<Self::Item<'a, As1: Copy>>;
LL +     fn next<'a>(&'a mut self) -> Option<Self::Item<'a>>;
   |

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0229`.