Macro impl_fill 

macro_rules! impl_fill {
    () => { ... };
    (to_le! plain $x:ident) => { ... };
    (to_le! wrapping $x:ident) => { ... };
    (fill_slice! $t:ty, $to_le:tt) => { ... };
    ($t:ty) => { ... };
    ($t:ty, $($tt:ty,)*) => { ... };
}

Implement Fill for given type $t.

Safety

All bit patterns of [u8; size_of::<$t>()] must represent values of $t.