alamb commented on code in PR #7812:
URL: https://github.com/apache/arrow-datafusion/pull/7812#discussion_r1356816885
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datafusion/physical-expr/src/physical_expr.rs:
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@@ -75,15 +75,49 @@ pub trait PhysicalExpr: Send + Sync + Display + Debug +
PartialEq<dyn Any> {
children: Vec<Arc<dyn PhysicalExpr>>,
) -> Result<Arc<dyn PhysicalExpr>>;
- /// Computes bounds for the expression using interval arithmetic.
+ /// Computes the output interval for the expression, given the input
+ /// intervals.
+ ///
+ /// # Arguments
+ ///
+ /// * `children` are the intervals for the children (inputs) of this
+ /// expression.
+ ///
+ /// # Example
+ ///
+ /// If the expression is `a + b`, and the input intervals are `a: [1, 2]`
+ /// and `b: [3, 4]`, then the output interval would be `[4, 6]`.
fn evaluate_bounds(&self, _children: &[&Interval]) -> Result<Interval> {
not_impl_err!("Not implemented for {self}")
}
- /// Updates/shrinks bounds for the expression using interval arithmetic.
+ /// Updates bounds for child expressions, given a known interval for this
+ /// expression.
+ ///
+ /// This is used to propagate constraints down through an
+ /// expression tree.
+ ///
+ /// # Arguments
+ ///
+ /// * `interval` is the currently known interval for this expression.
+ /// * `children` are the current intervals for the children of this
expression
+ ///
+ /// # Returns
+ ///
+ /// A Vec of new intervals for the children, in order.
+ ///
/// If constraint propagation reveals an infeasibility, returns [None] for
- /// the child causing infeasibility. If none of the children intervals
- /// change, may return an empty vector instead of cloning `children`.
+ /// the child causing infeasibility.
+ ///
+ /// If none of the child intervals change as a result of propagation, may
+ /// return an empty vector instead of cloning `children`.
+ ///
+ /// # Example
Review Comment:
@metesynnada and @berkaysynnada -- I would appreciate it if you could
double check this example. I think this is the kind of thing
`propagate_constraints` can do, but I am not 100% sure I got the example correct
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