Closed
Description
I need a enum which is deserialized with serde from number: -1, 0 and 1.
When I try to use enum_number macro from official serde documentation I get this:
error: expected pattern, found `-1`
--> src/serde_utils.rs:37:32
|
37 | $( $value => Ok($name::$variant), )*
| ^^^^^^
error: aborting due to previous error
The code is very simple:
enum_number!(Change {
Down = -1,
None = 0,
Up = 1,
});
macro_rules! enum_number {
($name:ident { $($variant:ident = $value:expr, )* }) => {
#[allow(missing_docs)]
#[derive(Clone, Copy, Debug, Eq, PartialEq, Ord, PartialOrd)]
pub enum $name {
$($variant = $value,)*
}
impl serde::Serialize for $name {
fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
where S: serde::Serializer
{
// Serialize the enum as a i64.
serializer.serialize_i64(*self as i64)
}
}
impl<'de> serde::Deserialize<'de> for $name {
fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
where D: serde::Deserializer<'de>
{
struct Visitor;
impl<'de> serde::de::Visitor<'de> for Visitor {
type Value = $name;
fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
formatter.write_str("signed 64-bit integer")
}
fn visit_i64<E>(self, value: i64) -> Result<$name, E>
where E: serde::de::Error
{
// Rust does not come with a simple way of converting a
// number to an enum, so use a big `match`.
match value {
$( $value => Ok($name::$variant), )*
_ => Err(E::custom(
format!("unknown {} value: {}",
stringify!($name), value))),
}
}
}
// Deserialize the enum from a i64.
deserializer.deserialize_i64(Visitor)
}
}
}
}
If I change -1 to a positive number it compiles okay. I think it is a problem.