error[E0308]: mismatched types
  --> $DIR/issue-26480.rs:16:19
   |
LL |                   $arr.len() * size_of($arr[0]));
   |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `u64`, found `usize`
...
LL |     write!(hello);
   |     -------------- in this macro invocation
   |
   = note: this error originates in the macro `write` (in Nightly builds, run with -Z macro-backtrace for more info)
help: you can convert a `usize` to a `u64` and panic if the converted value doesn't fit
   |
LL |                   ($arr.len() * size_of($arr[0])).try_into().unwrap());
   |                   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

error[E0605]: non-primitive cast: `{integer}` as `()`
  --> $DIR/issue-26480.rs:22:19
   |
LL |     ($x:expr) => ($x as ())
   |                   ^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
...
LL |     cast!(2);
   |     --------- in this macro invocation
   |
   = note: this error originates in the macro `cast` (in Nightly builds, run with -Z macro-backtrace for more info)

error: aborting due to 2 previous errors

Some errors have detailed explanations: E0308, E0605.
For more information about an error, try `rustc --explain E0308`.