sdd commented on code in PR #320: URL: https://github.com/apache/iceberg-rust/pull/320#discussion_r1566362815
########## crates/iceberg/src/expr/visitors/bound_predicate_visitor.rs: ########## @@ -0,0 +1,317 @@ +// Licensed to the Apache Software Foundation (ASF) under one +// or more contributor license agreements. See the NOTICE file +// distributed with this work for additional information +// regarding copyright ownership. The ASF licenses this file +// to you under the Apache License, Version 2.0 (the +// "License"); you may not use this file except in compliance +// with the License. You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, +// software distributed under the License is distributed on an +// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +// KIND, either express or implied. See the License for the +// specific language governing permissions and limitations +// under the License. + +use crate::expr::{BoundPredicate, BoundReference, PredicateOperator}; +use crate::spec::Datum; +use crate::Result; +use fnv::FnvHashSet; + +pub(crate) enum OpLiteral<'a> { + Single(&'a Datum), + Set(&'a FnvHashSet<Datum>), +} + +/// A visitor for [`BoundPredicate`]s. Visits in post-order. +pub trait BoundPredicateVisitor { + /// The return type of this visitor + type T; + + /// Called after an `AlwaysTrue` predicate is visited + fn always_true(&mut self) -> Result<Self::T>; + + /// Called after an `AlwaysFalse` predicate is visited + fn always_false(&mut self) -> Result<Self::T>; + + /// Called after an `And` predicate is visited + fn and(&mut self, lhs: Self::T, rhs: Self::T) -> Result<Self::T>; + + /// Called after an `Or` predicate is visited + fn or(&mut self, lhs: Self::T, rhs: Self::T) -> Result<Self::T>; + + /// Called after a `Not` predicate is visited + fn not(&mut self, inner: Self::T) -> Result<Self::T>; + + /// Called after visiting a UnaryPredicate, BinaryPredicate, + /// or SetPredicate. Passes the predicate's operator in all cases, + /// as well as the term and literals in the case of binary and aet + /// predicates. + fn op( + &mut self, + op: PredicateOperator, + reference: &BoundReference, + literal: Option<OpLiteral>, + predicate: &BoundPredicate, + ) -> Result<Self::T>; +} + +/// Visits a [`BoundPredicate`] with the provided visitor, +/// in post-order +pub(crate) fn visit<V: BoundPredicateVisitor>( + visitor: &mut V, + predicate: &BoundPredicate, +) -> Result<V::T> { + match predicate { + BoundPredicate::AlwaysTrue => visitor.always_true(), + BoundPredicate::AlwaysFalse => visitor.always_false(), + BoundPredicate::And(expr) => { + let [left_pred, right_pred] = expr.inputs(); + + let left_result = visit(visitor, left_pred)?; + let right_result = visit(visitor, right_pred)?; + + visitor.and(left_result, right_result) + } + BoundPredicate::Or(expr) => { + let [left_pred, right_pred] = expr.inputs(); + + let left_result = visit(visitor, left_pred)?; + let right_result = visit(visitor, right_pred)?; + + visitor.or(left_result, right_result) + } + BoundPredicate::Not(expr) => { + let [inner_pred] = expr.inputs(); + + let inner_result = visit(visitor, inner_pred)?; + + visitor.not(inner_result) + } + BoundPredicate::Unary(expr) => visitor.op(expr.op(), expr.term(), None, predicate), Review Comment: > I think this is the nicest way since it leverages the visitor pattern as much as possible, but I also saw the discussion of having this on the {unary,binary,set} level. If you're not happy with this approach @Fokko, I'll wait until the three of you are in agreement and fix up to whatever you all decide on. I'm happy with the approach as-is after switching my original design to the approach proposed by @liurenjie1024 and @marvinlanhenke. > With Python it is easy to have a cache-all where if nothing matches, it just goes to that one, and then we raise an exception that we've encountered an unknown predicate. This way it is possible to add new expressions, but I don't think that would happen too often. With the approach in the PR, if a new Op gets added, you have three options available when implementing `BoundPredicateVisitor` for a struct (if I remove the `#[non_exhaustive]` macro from `PredicateOperator`): 1. Exhaustively specify a match arm for every Op. If another Op gets added, your BoundPredicateVisitor will no longer compile 2. Specify a default match arm, and call `panic!()` in it. When a new Op gets added, your code still compiles but you get a runtime crash if the visitor encounters the new operator 3. Specify a default match arm, and `return Err(NotImplemented)` in it. When a new Op gets added, your code still compiles but you will get a handleable error if you encounter the new operator - potentially failing an invocation but not taking the service down. That provides the capability that you mention from Python, as well as other options. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: issues-unsubscr...@iceberg.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: issues-unsubscr...@iceberg.apache.org For additional commands, e-mail: issues-h...@iceberg.apache.org
