Struct datafusion_optimizer::simplify_expressions::ConstEvaluator

pub struct ConstEvaluator<'a> { /* private fields */ }

Partially evaluate Exprs so constant subtrees are evaluated at plan time.

Note it does not handle algebraic rewrites such as (a or false) –> a, which is handled by [Simplifier]

let execution_props = ExecutionProps::new();
let mut const_evaluator = ConstEvaluator::try_new(&execution_props).unwrap();

// (1 + 2) + a
let expr = (lit(1) + lit(2)) + col("a");

// is rewritten to (3 + a);
let rewritten = expr.rewrite(&mut const_evaluator).unwrap();
assert_eq!(rewritten, lit(3) + col("a"));

Implementations

impl<'a> ConstEvaluator<'a>

pub fn try_new(execution_props: &'a ExecutionProps) -> Result<Self>

Create a new ConstantEvaluator. Session constants (such as the time for now() are taken from the passed execution_props.

Trait Implementations

impl<'a> ExprRewriter<Expr> for ConstEvaluator<'a>

fn pre_visit(&mut self, expr: &Expr) -> Result<RewriteRecursion>

Invoked before any children of expr are rewritten / visited. Default implementation returns Ok(RewriteRecursion::Continue)

fn mutate(&mut self, expr: Expr) -> Result<Expr>

Invoked after all children of expr have been mutated and returns a potentially modified expr.