custom_deserialize_serde.rs

use serde::de::{Deserialize, Deserializer, Error, Visitor};
use std::fmt;

use serde_json::de::from_str;

#[derive(Clone, Debug, Eq, PartialEq)]
enum YourFancyEnum {
  Foo,
  Bar,
  Zoo,
  Quux,
  Unknown(String)
}

impl<'de> Deserialize<'de> for YourFancyEnum {
  fn deserialize<D>(deserializer: D) -> Result<Self, D::Error> where D: Deserializer<'de> {
    struct V;

    impl<'de> Visitor<'de> for V {
      type Value = YourFancyEnum;

      fn expecting(&self, formatter: &mut fmt::Formatter) -> Result<(), fmt::Error> {
        formatter.write_str("Foo, Bar, Zoo, Quux or any unknown string")
      }

      fn visit_str<E>(self, s: &str) -> Result<Self::Value, E> where E: Error {
        match &s[..] {
          "Foo" => Ok(YourFancyEnum::Foo),
          "Bar" => Ok(YourFancyEnum::Bar),
          "Zoo" => Ok(YourFancyEnum::Zoo),
          "Quux" => Ok(YourFancyEnum::Quux),
          _ => Ok(YourFancyEnum::Unknown(s.to_owned()))
        }
      }
    }

    deserializer.deserialize_str(V)
  }
}

fn main() {
  println!("{:?}", from_str::<YourFancyEnum>(r#""Foo""#));
  println!("{:?}", from_str::<YourFancyEnum>(r#""Bar""#));
  println!("{:?}", from_str::<YourFancyEnum>(r#""Zoo""#));
  println!("{:?}", from_str::<YourFancyEnum>(r#""Quux""#));
  println!("{:?}", from_str::<YourFancyEnum>(r#""Warghl""#));
}