cco 0.2.0

cascading configuration
Documentation 
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use super::{Expr, ExprEvaluator};
use crate::err::*;
use crate::eval::*;
use crate::value::*;

#[derive(Debug, Clone)]
pub struct TypeGuardExpr {
    pub expr: Index,
    pub ty: ValueKind,
}

impl Expr for TypeGuardExpr {
    fn resolve(
        &self,
        index: Index,
        evaluation: &mut dyn ExprEvaluator,
    ) -> Result<ValueOrReference, ErrorKind> {
        evaluation.ensure_resolved(vec![self.expr])?;

        let value = evaluation.get_value(self.expr)?;
        if value.kind() != self.ty {
            return Err(ErrorKind::TypeNotAllowed {
                item: index,
                expr: self.expr,
                expected: self.ty,
                actual: value.kind(),
            })?;
        }
        Ok(value.into())
    }

    fn traverse(
        &self,
        _evaluation: &dyn ExprEvaluator,
        expression: Index,
        _name: &Indexer,
    ) -> Result<Option<ValueOrReference>, ErrorKind> {
        Err(ErrorKind::DependenciesNotSatisfied {
            indices: vec![expression],
        })
    }
}