Struct UnionParser 

pub struct UnionParser<'doc, T> { /* private fields */ }

Helper for parsing union types from Eure documents.

Implements oneOf semantics:

• Exactly one variant must match
• Multiple matches resolved by registration order (priority)
• Short-circuits on first priority variant match
• When $variant extension is specified, matches by name directly

Example

impl ParseDocument<'_> for Description {
    fn parse(doc: &EureDocument, node_id: NodeId) -> Result<Self, ParseError> {
        doc.parse_union(node_id)
            .variant("string", |doc, id| {
                let text: String = doc.parse(id)?;
                Ok(Description::String(text))
            })
            .variant("markdown", |doc, id| {
                let text: String = doc.parse(id)?;
                Ok(Description::Markdown(text))
            })
            .parse()
    }
}

Implementations

impl<'doc, T> UnionParser<'doc, T>

pub fn variant<P>(self, name: &str, parser: P) -> Self

where P: DocumentParser<'doc, Output = T> + 'doc,

Register a priority variant.

Priority variants are tried in registration order. When a priority variant matches, parsing short-circuits and returns immediately.

pub fn other<P>(self, name: &str, parser: P) -> Self

where P: DocumentParser<'doc, Output = T> + 'doc,

Register a non-priority variant.

Non-priority variants are only tried if no priority variant matches. All non-priority variants are tried to detect ambiguity.

pub fn parse(self) -> Result<T, ParseError>

Execute the union parse with oneOf semantics.

Returns:

• Ok(T) if exactly one variant matches (or priority resolves ambiguity)
• Err(UnknownVariant) if $variant specifies an unregistered name
• Err(NoMatchingVariant) if no variants match
• Err(AmbiguousUnion) if multiple non-priority variants match