use serde::de::{self, Deserializer};
use serde::Deserialize;

fn main() {}

struct Duration {
    secs: u64,
    nanos: u32,
}

impl<'de> de::Deserialize<'de> for Duration {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: Deserializer<'de>,
    {
        // Comment out these lines and uncomment the manual impl of Deserialize
        // to make it work
        #[derive(Deserialize)]
        enum Field { Secs, Nanos }

//        enum Field { Secs, Nanos };
//
//        impl<'de> Deserialize<'de> for Field {
//            fn deserialize<D>(deserializer: D) -> Result<Field, D::Error>
//            where
//                D: Deserializer<'de>,
//            {
//                struct FieldVisitor;
//
//                impl<'de> Visitor<'de> for FieldVisitor {
//                    type Value = Field;
//
//                    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
//                        formatter.write_str("`secs` or `nanos`")
//                    }
//
//                    fn visit_str<E>(self, value: &str) -> Result<Field, E>
//                    where
//                        E: de::Error,
//                    {
//                        match value {
//                            "Secs" => Ok(Field::Secs),
//                            "Nanos" => Ok(Field::Nanos),
//                            _ => Err(de::Error::unknown_field(value, FIELDS)),
//                        }
//                    }
//                }
//
//                deserializer.deserialize_identifier(FieldVisitor)
//            }
//        }

    }
}