serde.rs

struct ParseVisitor<T> { 
    _marker: PhantomData<T>   
}

impl<'de, T> Visitor<'de> for ParseVisitor<T>
    where T: std::str::FromStr 
{
    type Value = T;

    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        formatter.write_str("a string object that parses to T")
    }

    fn visit_str<E>(self, s: &str) -> Result<Self::Value, E>
        where E: de::Error,
    {
        if let Ok(t) = s.parse::<T>() {
            Ok(t)
        }
        else {
            Err(de::Error::invalid_value(Unexpected::Str(s), &self))
        }
    }
}

fn deserialize_parse<'de, T, D>(deserializer: D) -> Result<T, D::Error>
    where D: Deserializer<'de>, T: str::FromStr 
{
    deserializer.deserialize_string(ParseVisitor::<T> { _marker: PhantomData })      
}

#[derive(Debug, Deserialize)]
struct Stream {
    #[serde(deserialize_with="deserialize_parse")]
    id: u64,
    #[serde(deserialize_with="deserialize_parse")]
    user_id: u64,
    #[serde(deserialize_with="deserialize_parse")]
    game_id: u64,
    title: String,
}