example code of custom serialization/deserialization

serde_custom.rs

#[derive(Eq, PartialEq, Clone)]
pub struct ToolVersion(Version);

impl Serialize for ToolVersion {
    fn serialize<S: Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
        let &ToolVersion(ref version) = self;
        let unparsed = format!("{}", version);
        serializer.serialize_str(&unparsed[..])
    }
}

struct ToolVersionVisitor;

impl<'de> Visitor<'de> for ToolVersionVisitor {
    type Value = ToolVersion;

    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        formatter.write_str("a semver version string")
    }

    fn visit_str<E: de::Error>(self, v: &str) -> Result<Self::Value, E> {
        Version::parse(v)
            .map(ToolVersion)
            .map_err(|e| E::custom(format!("{}", e)))
    }
}

impl<'de> Deserialize<'de> for ToolVersion {
    fn deserialize<D: Deserializer<'de>>(deserializer: D) -> Result<ToolVersion, D::Error> {
        deserializer.deserialize_str(ToolVersionVisitor)
    }
}