error[E0615]: attempted to take value of method `speak` on type `Cat`
  --> $DIR/assign-to-method.rs:22:10
   |
LL |     nyan.speak = || println!("meow");
   |          ^^^^^ method, not a field
   |
   = help: methods are immutable and cannot be assigned to

error[E0615]: attempted to take value of method `speak` on type `Cat`
  --> $DIR/assign-to-method.rs:23:10
   |
LL |     nyan.speak += || println!("meow");
   |          ^^^^^ method, not a field
   |
   = help: methods are immutable and cannot be assigned to

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0615`.