Extracting struct name from Value?

[jgarvin]

Looking at the docs for Value:

pub enum Value {
    Bool(bool),
    Char(char),
    Map(Map),
    Number(Number),
    Option(Option<Box<Value>>),
    String(String),
    Seq(Vec<Value>),
    Unit,
}

I don't see how to get the name of a struct out, e.g. if I were to call from_str on the contents of example.ron, how would I get the string "Nested" out of it? My use case is the following: I want to have a field that could be one of many different structs. I'd like to parse into a ron Value, check the parsed struct name, then based on that name choose which actual T to pass to into_rust. I couldn't find this in the examples/docs.

[jgarvin]

So I spent some time playing around with adding:

#[derive(Clone, Debug, Default, Deserialize, Serialize, Eq)]
pub struct Structure {
    pub name: String,
    pub fields: Map,
}

impl Hash for Structure {
    fn hash<H: Hasher>(&self, state: &mut H) {
        // TODO: is this any different than #derive'ing Hash?
        self.name.hash(state);
        self.fields.hash(state);
    }
}

impl Ord for Structure {
    fn cmp(&self, other: &Structure) -> Ordering {
        (&self.name, &self.fields).cmp(&(&other.name, &other.fields))
    }
}

/// Note: equality is only given name matches and if both values and order of values match
impl PartialEq for Structure {
    fn eq(&self, other: &Structure) -> bool {
        self.name == other.name && self.fields == other.fields
    }
}

impl PartialOrd for Structure {
    fn partial_cmp(&self, other: &Structure) -> Option<Ordering> {
        (&self.name, &self.fields).partial_cmp(&(&other.name, &other.fields))
    }
}

#[derive(Clone, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
pub enum Value {
    Bool(bool),
    Char(char),
    Structure(Structure),
    Map(Map),
    Number(Number),
    Option(Option<Box<Value>>),
    String(String),
    Seq(Vec<Value>),
    Unit,
}

But the problem I'm running into is that serde's data model seems to force losing struct names when combined with the lack of a parser separate from serde. What I see:

• parse.rs doesn't give a full parser, it appears to be utility functions for implementing one
• Deserializer actually contains the parser, and uses the parse.rs functions.
• Deserializer needs you to map the input onto the serde data model.
• The data model doesn't support struct names, so it's lost.
• Deserialize translates the serde data model into the data structure, but it's too late, it only sees a map.

I think in order for this to work there has to be a parser independent of any use of serde that can translate text streams into RON Values.

[kvark]

If that's something Serde lacks, but is needed, would there be an upstream issue about this?

[jgarvin]

I found serde-rs/serde#1345 which suggests wrapping in a struct with one field that is the name of the actual struct. They link to a helper crate that a later commenter says is broken though.

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