Trait datafusion_expr::PlanVisitor

source · [−]
pub trait PlanVisitor {
    type Error;

    fn pre_visit(&mut self, plan: &LogicalPlan) -> Result<bool, Self::Error>;

    fn post_visit(&mut self, _plan: &LogicalPlan) -> Result<bool, Self::Error> { ... }
}
Expand description

Trait that implements the Visitor pattern for a depth first walk of LogicalPlan nodes. pre_visit is called before any children are visited, and then post_visit is called after all children have been visited. To use, define a struct that implements this trait and then invoke LogicalPlan::accept.

For example, for a logical plan like:

Projection: #id
   Filter: #state Eq Utf8(\"CO\")\
      CsvScan: employee.csv projection=Some([0, 3])";

The sequence of visit operations would be:

visitor.pre_visit(Projection)
visitor.pre_visit(Filter)
visitor.pre_visit(CsvScan)
visitor.post_visit(CsvScan)
visitor.post_visit(Filter)
visitor.post_visit(Projection)

Required Associated Types

The type of error returned by this visitor

Required Methods

Invoked on a logical plan before any of its child inputs have been visited. If Ok(true) is returned, the recursion continues. If Err(..) or Ok(false) are returned, the recursion stops immediately and the error, if any, is returned to accept

Provided Methods

Invoked on a logical plan after all of its child inputs have been visited. The return value is handled the same as the return value of pre_visit. The provided default implementation returns Ok(true).

Implementors