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rustc -C opt-level=3 2.rs
error[E0277]: expected a `std::ops::Fn<()>` closure, found `std::boxed::Box<[closure@2.rs:12:24: 12:43]>`
  --> 2.rs:16:17
   |
16 |         bx_cl = Box::new(cl1.clone());
   |                 ^^^^^^^^^^^^^^^^^^^^^ expected an `Fn<()>` closure, found `std::boxed::Box<[closure@2.rs:12:24: 12:43]>`
   |
   = help: the trait `std::ops::Fn<()>` is not implemented for `std::boxed::Box<[closure@2.rs:12:24: 12:43]>`
   = note: wrap the `std::boxed::Box<[closure@2.rs:12:24: 12:43]>` in a closure with no arguments: `|| { /* code */ }
   = note: required for the cast to the object type `dyn std::ops::Fn()`

error[E0277]: expected a `std::ops::Fn<()>` closure, found `std::boxed::Box<[closure@2.rs:13:24: 13:44]>`
  --> 2.rs:18:17
   |
18 |         bx_cl = Box::new(cl2.clone());
   |                 ^^^^^^^^^^^^^^^^^^^^^ expected an `Fn<()>` closure, found `std::boxed::Box<[closure@2.rs:13:24: 13:44]>`
   |
   = help: the trait `std::ops::Fn<()>` is not implemented for `std::boxed::Box<[closure@2.rs:13:24: 13:44]>`
   = note: wrap the `std::boxed::Box<[closure@2.rs:13:24: 13:44]>` in a closure with no arguments: `|| { /* code */ }
   = note: required for the cast to the object type `dyn std::ops::Fn()`

error[E0277]: expected a `std::ops::Fn<()>` closure, found `std::boxed::Box<[closure@2.rs:20:24: 20:37 cl1:_]>`
  --> 2.rs:24:18
   |
24 |         bx_cl2 = Box::new(cl3);
   |                  ^^^^^^^^^^^^^ expected an `Fn<()>` closure, found `std::boxed::Box<[closure@2.rs:20:24: 20:37 cl1:_]>`
   |
   = help: the trait `std::ops::Fn<()>` is not implemented for `std::boxed::Box<[closure@2.rs:20:24: 20:37 cl1:_]>`
   = note: wrap the `std::boxed::Box<[closure@2.rs:20:24: 20:37 cl1:_]>` in a closure with no arguments: `|| { /* code */ }
   = note: required for the cast to the object type `dyn std::ops::Fn()`

error[E0277]: expected a `std::ops::Fn<()>` closure, found `std::boxed::Box<[closure@2.rs:21:24: 21:37 cl2:_]>`
  --> 2.rs:26:18
   |
26 |         bx_cl2 = Box::new(cl4);
   |                  ^^^^^^^^^^^^^ expected an `Fn<()>` closure, found `std::boxed::Box<[closure@2.rs:21:24: 21:37 cl2:_]>`
   |
   = help: the trait `std::ops::Fn<()>` is not implemented for `std::boxed::Box<[closure@2.rs:21:24: 21:37 cl2:_]>`
   = note: wrap the `std::boxed::Box<[closure@2.rs:21:24: 21:37 cl2:_]>` in a closure with no arguments: `|| { /* code */ }
   = note: required for the cast to the object type `dyn std::ops::Fn()`

error: aborting due to 4 previous errors

For more information about this error, try `rustc --explain E0277`.
fsb4000@orangepilite2:~/rust$ rustc -V
rustc 1.34.2

rustc -C opt-level=3 2.rs
error[E0277]: expected a `std::ops::Fn<()>` closure, found `std::boxed::Box<[closure@2.rs:12:24: 12:43]>`
  --> 2.rs:16:17
   |
16 |         bx_cl = Box::new(cl1.clone());
   |                 ^^^^^^^^^^^^^^^^^^^^^ expected an `Fn<()>` closure, found `std::boxed::Box<[closure@2.rs:12:24: 12:43]>`
   |
   = help: the trait `std::ops::Fn<()>` is not implemented for `std::boxed::Box<[closure@2.rs:12:24: 12:43]>`
   = note: wrap the `std::boxed::Box<[closure@2.rs:12:24: 12:43]>` in a closure with no arguments: `|| { /* code */ }
   = note: required for the cast to the object type `dyn std::ops::Fn()`

error[E0277]: expected a `std::ops::Fn<()>` closure, found `std::boxed::Box<[closure@2.rs:13:24: 13:44]>`
  --> 2.rs:18:17
   |
18 |         bx_cl = Box::new(cl2.clone());
   |                 ^^^^^^^^^^^^^^^^^^^^^ expected an `Fn<()>` closure, found `std::boxed::Box<[closure@2.rs:13:24: 13:44]>`
   |
   = help: the trait `std::ops::Fn<()>` is not implemented for `std::boxed::Box<[closure@2.rs:13:24: 13:44]>`
   = note: wrap the `std::boxed::Box<[closure@2.rs:13:24: 13:44]>` in a closure with no arguments: `|| { /* code */ }
   = note: required for the cast to the object type `dyn std::ops::Fn()`

error[E0277]: expected a `std::ops::Fn<()>` closure, found `std::boxed::Box<[closure@2.rs:20:24: 20:37 cl1:_]>`
  --> 2.rs:24:18
   |
24 |         bx_cl2 = Box::new(cl3);
   |                  ^^^^^^^^^^^^^ expected an `Fn<()>` closure, found `std::boxed::Box<[closure@2.rs:20:24: 20:37 cl1:_]>`
   |
   = help: the trait `std::ops::Fn<()>` is not implemented for `std::boxed::Box<[closure@2.rs:20:24: 20:37 cl1:_]>`
   = note: wrap the `std::boxed::Box<[closure@2.rs:20:24: 20:37 cl1:_]>` in a closure with no arguments: `|| { /* code */ }
   = note: required for the cast to the object type `dyn std::ops::Fn()`

error[E0277]: expected a `std::ops::Fn<()>` closure, found `std::boxed::Box<[closure@2.rs:21:24: 21:37 cl2:_]>`
  --> 2.rs:26:18
   |
26 |         bx_cl2 = Box::new(cl4);
   |                  ^^^^^^^^^^^^^ expected an `Fn<()>` closure, found `std::boxed::Box<[closure@2.rs:21:24: 21:37 cl2:_]>`
   |
   = help: the trait `std::ops::Fn<()>` is not implemented for `std::boxed::Box<[closure@2.rs:21:24: 21:37 cl2:_]>`
   = note: wrap the `std::boxed::Box<[closure@2.rs:21:24: 21:37 cl2:_]>` in a closure with no arguments: `|| { /* code */ }
   = note: required for the cast to the object type `dyn std::ops::Fn()`

error: aborting due to 4 previous errors

For more information about this error, try `rustc --explain E0277`.
fsb4000@orangepilite2:~/rust$ rustc -V
rustc 1.34.2