1#[macro_export] 2macro_rules! from_err { 3 ($from:ty, $to:tt, $var:tt) => { 4 impl From<$from> for $to { 5 #[inline] 6 fn from(e: $from) -> $to { 7 $to::$var(e) 8 } 9 } 10 }; 11}