com.google.gerrit.index.query.Predicate Maven / Gradle / Ivy
// Copyright (C) 2009 The Android Open Source Project
//
// Licensed 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.
package com.google.gerrit.index.query;
import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkState;
import com.google.common.collect.Iterables;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
/**
* An abstract predicate tree for any form of query.
*
* Implementations should be immutable, such that the meaning of a predicate never changes once
* constructed. They should ensure their immutable promise by defensively copying any structures
* which might be modified externally, but was passed into the object's constructor.
*
*
However, implementations may retain non-thread-safe caches internally, to speed up
* evaluation operations within the context of one thread's evaluation of the predicate. As a
* result, callers should assume predicates are not thread-safe, but that two predicate graphs
* produce the same results given the same inputs if they are {@link #equals(Object)}.
*
*
Predicates should support deep inspection whenever possible, so that generic algorithms can be
* written to operate against them. Predicates which contain other predicates should override {@link
* #getChildren()} to return the list of children nested within the predicate.
*
* @param type of object the predicate can evaluate in memory.
*/
public abstract class Predicate {
/** A predicate that matches any input, always, with no cost. */
@SuppressWarnings("unchecked")
public static Predicate any() {
return (Predicate) Any.INSTANCE;
}
/** Combine the passed predicates into a single AND node. */
@SafeVarargs
public static Predicate and(Predicate... that) {
if (that.length == 1) {
return that[0];
}
return new AndPredicate<>(that);
}
/** Combine the passed predicates into a single AND node. */
public static Predicate and(Collection> that) {
if (that.size() == 1) {
return Iterables.getOnlyElement(that);
}
return new AndPredicate<>(that);
}
/** Combine the passed predicates into a single OR node. */
@SafeVarargs
public static Predicate or(Predicate... that) {
if (that.length == 1) {
return that[0];
}
return new OrPredicate<>(that);
}
/** Combine the passed predicates into a single OR node. */
public static Predicate or(Collection> that) {
if (that.size() == 1) {
return Iterables.getOnlyElement(that);
}
return new OrPredicate<>(that);
}
/** Invert the passed node. */
public static Predicate not(Predicate that) {
checkArgument(
!(that instanceof Any), "negating any() is unsafe because it post-filters all results");
if (that instanceof NotPredicate) {
// Negate of a negate is the original predicate.
//
return that.getChild(0);
}
return new NotPredicate<>(that);
}
/** Get the children of this predicate, if any. */
public List> getChildren() {
return Collections.emptyList();
}
/** Same as {@code getChildren().size()} */
public int getChildCount() {
return getChildren().size();
}
/** Same as {@code getChildren().get(i)} */
public Predicate getChild(int i) {
return getChildren().get(i);
}
/** Get the number of leaf terms in this predicate. */
public int getLeafCount() {
int leafCount = 0;
for (Predicate childPredicate : getChildren()) {
if (childPredicate instanceof IndexPredicate) {
leafCount++;
}
leafCount += childPredicate.getLeafCount();
}
return leafCount;
}
/** Create a copy of this predicate, with new children. */
public abstract Predicate copy(Collection> children);
public boolean isMatchable() {
return this instanceof Matchable;
}
@SuppressWarnings("unchecked")
public Matchable asMatchable() {
checkState(isMatchable(), "not matchable");
return (Matchable) this;
}
/** @return a cost estimate to run this predicate, higher figures cost more. */
public int estimateCost() {
if (!isMatchable()) {
return 1;
}
return asMatchable().getCost();
}
@Override
public abstract int hashCode();
@Override
public abstract boolean equals(Object other);
private static class Any extends Predicate implements Matchable {
private static final Any