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/*
Copyright ⓒ 2015 macro-attr contributors.
Licensed under the MIT license (see LICENSE or <http://opensource.org
/licenses/MIT>) or the Apache License, Version 2.0 (see LICENSE of
<http://www.apache.org/licenses/LICENSE-2.0>), at your option. All
files in the project carrying such notice may not be copied, modified,
or distributed except according to those terms.
*/
#[macro_use] extern crate macro_attr;
trait TryFrom<Src>: Sized {
type Err;
fn try_from(src: Src) -> Result<Self, Self::Err>;
}
macro_rules! TryFrom {
(($prim:ty) $(pub)* enum $name:ident { $($body:tt)* }) => {
TryFrom! {
@collect_variants ($name, $prim),
($($body)*,) -> ()
}
};
(
@collect_variants ($name:ident, $prim:ty),
($(,)*) -> ($($var_names:ident,)*)
) => {
impl TryFrom<$prim> for $name {
type Err = $prim;
fn try_from(src: $prim) -> Result<$name, $prim> {
$(
if src == $name::$var_names as $prim {
return Ok($name::$var_names);
}
)*
Err(src)
}
}
};
(
@collect_variants $fixed:tt,
($var:ident $(= $_val:expr)*, $($tail:tt)*) -> ($($var_names:tt)*)
) => {
TryFrom! {
@collect_variants $fixed,
($($tail)*) -> ($($var_names)* $var,)
}
};
(
@collect_variants ($name:ident),
($var:ident $_struct:tt, $($tail:tt)*) -> ($($var_names:tt)*)
) => {
const _error: () = concat!(
"cannot derive TryFrom for ",
stringify!($name),
", due to non-unitary variant ",
stringify!($var),
"."
);
};
}
macro_attr! {
#[derive(Debug, PartialEq, TryFrom!(u8))]
enum Get { Up, Down, AllAround }
}
#[test]
fn test_try_from() {
assert_eq!(Get::try_from(0u8), Ok(Get::Up));
assert_eq!(Get::try_from(1u8), Ok(Get::Down));
assert_eq!(Get::try_from(2u8), Ok(Get::AllAround));
assert_eq!(Get::try_from(3u8), Err(3u8));
}
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