Method cast_to

datafusion/expr/src/expr_schema.rs:686–715

Wraps this expression in a cast to a target [arrow::datatypes::DataType]. # Errors This function errors when it is impossible to cast the expression to the target [arrow::datatypes::DataType].

(self, cast_to_type: &DataType, schema: &dyn ExprSchema)

    /// This function errors when it is impossible to cast the
    /// expression to the target [arrow::datatypes::DataType].
    fn cast_to(self, cast_to_type: &DataType, schema: &dyn ExprSchema) -> Result<Expr> {
        let this_type = self.get_type(schema)?;
        if this_type == *cast_to_type {
            return Ok(self);
        }

        // TODO(kszucs): Most of the operations do not validate the type correctness
        // like all of the binary expressions below. Perhaps Expr should track the
        // type of the expression?

        // Special handling for struct-to-struct casts with name-based field matching
        let can_cast = match (&this_type, cast_to_type) {
            (DataType::Struct(_), DataType::Struct(_)) => {
                // Always allow struct-to-struct casts; field matching happens at runtime
                true
            }
            _ => can_cast_types(&this_type, cast_to_type),
        };

        if can_cast {
            match self {
                Expr::ScalarSubquery(subquery) => {
                    Ok(Expr::ScalarSubquery(cast_subquery(subquery, cast_to_type)?))
                }
                _ => Ok(Expr::Cast(Cast::new(Box::new(self), cast_to_type.clone()))),
            }
        } else {
            plan_err!("Cannot automatically convert {this_type} to {cast_to_type}")
        }
    }
}

/// Verify that function is invoked with correct number and type of arguments as