error[E0606]: casting `&[i32]` as `usize` is invalid
  --> $DIR/fat-ptr-cast.rs:20:5
   |
LL |     a as usize; //~ ERROR casting
   |     ^^^^^^^^^^
   |
   = help: cast through a raw pointer first

error[E0606]: casting `&[i32]` as `isize` is invalid
  --> $DIR/fat-ptr-cast.rs:21:5
   |
LL |     a as isize; //~ ERROR casting
   |     ^^^^^^^^^^
   |
   = help: cast through a raw pointer first

error[E0606]: casting `&[i32]` as `i16` is invalid
  --> $DIR/fat-ptr-cast.rs:22:5
   |
LL |     a as i16; //~ ERROR casting `&[i32]` as `i16` is invalid
   |     ^^^^^^^^
   |
   = help: cast through a raw pointer first

error[E0606]: casting `&[i32]` as `u32` is invalid
  --> $DIR/fat-ptr-cast.rs:23:5
   |
LL |     a as u32; //~ ERROR casting `&[i32]` as `u32` is invalid
   |     ^^^^^^^^
   |
   = help: cast through a raw pointer first

error[E0605]: non-primitive cast: `std::boxed::Box<[i32]>` as `usize`
  --> $DIR/fat-ptr-cast.rs:24:5
   |
LL |     b as usize; //~ ERROR non-primitive cast
   |     ^^^^^^^^^^
   |
   = note: an `as` expression can only be used to convert between primitive types. Consider using the `From` trait

error[E0606]: casting `*const [i32]` as `usize` is invalid
  --> $DIR/fat-ptr-cast.rs:25:5
   |
LL |     p as usize;
   |     ^^^^^^^^^^
   |
   = help: cast through a thin pointer first

error[E0607]: cannot cast thin pointer `*const i32` to fat pointer `*const [i32]`
  --> $DIR/fat-ptr-cast.rs:29:5
   |
LL |     q as *const [i32]; //~ ERROR cannot cast
   |     ^^^^^^^^^^^^^^^^^

error[E0606]: casting `usize` as `*mut Trait + 'static` is invalid
  --> $DIR/fat-ptr-cast.rs:32:37
   |
LL |     let t: *mut (Trait + 'static) = 0 as *mut _; //~ ERROR casting
   |                                     ^^^^^^^^^^^

error[E0606]: casting `usize` as `*const str` is invalid
  --> $DIR/fat-ptr-cast.rs:33:32
   |
LL |     let mut fail: *const str = 0 as *const str; //~ ERROR casting
   |                                ^^^^^^^^^^^^^^^

error: aborting due to 9 previous errors

You've got a few errors: E0605, E0606, E0607
If you want more information on an error, try using "rustc --explain E0605"