error[E0019]: constant function contains unimplemented expression type
  --> $DIR/const_let_assign3.rs:9:9
   |
LL |         self.state = x;
   |         ^^^^^^^^^^^^^^

error[E0017]: references in constants may only refer to immutable values
  --> $DIR/const_let_assign3.rs:16:5
   |
LL |     s.foo(3); //~ ERROR references in constants may only refer to immutable values
   |     ^ constants require immutable values

error[E0017]: references in constants may only refer to immutable values
  --> $DIR/const_let_assign3.rs:22:13
   |
LL |     let y = &mut x;
   |             ^^^^^^ constants require immutable values

error[E0019]: constant contains unimplemented expression type
  --> $DIR/const_let_assign3.rs:24:5
   |
LL |     *y = 42;
   |     ^^^^^^^

error: aborting due to 4 previous errors

Some errors occurred: E0017, E0019.
For more information about an error, try `rustc --explain E0017`.