substrait_explain::parser::relations

Function expect_one_child

Source 
pub(crate) fn expect_one_child(
    message: &'static str,
    pair: &Pair<'_, Rule>,
    input_children: Vec<Box<Rel>>,
) -> Result<Box<Rel>, MessageParseError>
Expand description

This is a utility function for extracting a single child from the list of children, to be used in the RelationParsePair trait. The RelationParsePair trait passes a Vec of children, because some relations have multiple children - but most accept exactly one child.