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Implement filter, map, reduce (#1031)
JAVA-4781
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‎driver-core/src/main/com/mongodb/client/model/expressions/ArrayExpression.java

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package com.mongodb.client.model.expressions;
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import java.util.function.BinaryOperator;
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import java.util.function.Function;
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/**
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* Expresses an array value. An array value is a finite, ordered collection of
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* elements of a certain type.
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*/
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public interface ArrayExpression<T extends Expression> extends Expression {
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/**
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* Returns an array consisting of those elements in this array that match
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* the given predicate condition. Evaluates each expression in this array
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* according to the cond function. If cond evaluates to logical true, then
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* the element is preserved; if cond evaluates to logical false, the element
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* is omitted.
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*
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* @param cond the function to apply to each element
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* @return the new array
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*/
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ArrayExpression<T> filter(Function<? super T, ? extends BooleanExpression> cond);
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/**
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* Returns an array consisting of the results of applying the given function
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* to the elements of this array.
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*
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* @param in the function to apply to each element
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* @return the new array
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* @param <R> the type contained in the resulting array
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*/
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<R extends Expression> ArrayExpression<R> map(Function<? super T, ? extends R> in);
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/**
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* Performs a reduction on the elements of this array, using the provided
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* identity value and an associative reducing function, and returns
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* the reduced value. The initial value must be the identity value for the
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* reducing function.
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*
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* @param initialValue the identity for the reducing function
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* @param in the associative reducing function
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* @return the reduced value
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*/
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T reduce(T initialValue, BinaryOperator<T> in);
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}

‎driver-core/src/main/com/mongodb/client/model/expressions/Expressions.java

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package com.mongodb.client.model.expressions;
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import org.bson.BsonArray;
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import org.bson.BsonBoolean;
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import org.bson.BsonInt32;
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import org.bson.BsonString;
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import org.bson.BsonValue;
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import java.util.ArrayList;
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import java.util.List;
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/**
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* Convenience methods related to {@link Expression}.
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public static StringExpression of(final String of) {
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return new MqlExpression<>((codecRegistry) -> new BsonString(of));
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}
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/**
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* Returns an array expression containing the same boolean values as the
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* provided array of booleans.
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*
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* @param array the array of booleans
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* @return the boolean array expression
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*/
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public static ArrayExpression<BooleanExpression> ofBooleanArray(final boolean... array) {
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List<BsonValue> result = new ArrayList<>();
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for (boolean b : array) {
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result.add(new BsonBoolean(b));
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}
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return new MqlExpression<>((cr) -> new BsonArray(result));
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}
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}

‎driver-core/src/main/com/mongodb/client/model/expressions/MqlExpression.java

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import org.bson.BsonValue;
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import org.bson.codecs.configuration.CodecRegistry;
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import java.util.function.BinaryOperator;
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import java.util.function.Function;
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final class MqlExpression<T extends Expression>
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return newMqlExpression(ast("$cond", left, right));
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}
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/** @see ArrayExpression */
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@Override
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public <R extends Expression> ArrayExpression<R> map(final Function<? super T, ? extends R> in) {
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T varThis = variable("$$this");
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return new MqlExpression<>((cr) -> astDoc("$map", new BsonDocument()
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.append("input", this.toBsonValue(cr))
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.append("in", extractBsonValue(cr, in.apply(varThis)))).apply(cr));
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}
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@Override
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public ArrayExpression<T> filter(final Function<? super T, ? extends BooleanExpression> cond) {
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T varThis = variable("$$this");
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return new MqlExpression<T>((cr) -> astDoc("$filter", new BsonDocument()
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.append("input", this.toBsonValue(cr))
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.append("cond", extractBsonValue(cr, cond.apply(varThis)))).apply(cr));
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}
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@Override
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public T reduce(final T initialValue, final BinaryOperator<T> in) {
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T varThis = variable("$$this");
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T varValue = variable("$$value");
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return newMqlExpression((cr) -> astDoc("$reduce", new BsonDocument()
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.append("input", this.toBsonValue(cr))
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.append("initialValue", extractBsonValue(cr, initialValue))
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.append("in", extractBsonValue(cr, in.apply(varThis, varValue)))).apply(cr));
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}
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}

‎driver-core/src/test/functional/com/mongodb/client/model/expressions/ArrayExpressionsFunctionalTest.java

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/*
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* Copyright 2008-present MongoDB, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.mongodb.client.model.expressions;
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import org.junit.jupiter.api.Test;
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import java.util.Arrays;
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import java.util.stream.Collectors;
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import java.util.stream.Stream;
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import static com.mongodb.client.model.expressions.Expressions.of;
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import static com.mongodb.client.model.expressions.Expressions.ofBooleanArray;
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@SuppressWarnings({"PointlessBooleanExpression", "ConstantConditions", "Convert2MethodRef"})
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class ArrayExpressionsFunctionalTest extends AbstractExpressionsFunctionalTest {
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// https://www.mongodb.com/docs/manual/reference/operator/aggregation/#array-expression-operators
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// (Incomplete)
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private final ArrayExpression<BooleanExpression> arrayTTF = ofBooleanArray(true, true, false);
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@Test
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public void literalsTest() {
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assertExpression(Arrays.asList(true, true, false), arrayTTF, "[true, true, false]");
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}
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@Test
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public void filterTest() {
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// https://www.mongodb.com/docs/manual/reference/operator/aggregation/filter/
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assertExpression(
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Stream.of(true, true, false)
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.filter(v -> v).collect(Collectors.toList()),
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arrayTTF.filter(v -> v),
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// MQL:
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"{'$filter': {'input': [true, true, false], 'cond': '$$this'}}");
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}
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@Test
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public void mapTest() {
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// https://www.mongodb.com/docs/manual/reference/operator/aggregation/map/
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assertExpression(
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Stream.of(true, true, false)
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.map(v -> !v).collect(Collectors.toList()),
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arrayTTF.map(v -> v.not()),
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// MQL:
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"{'$map': {'input': [true, true, false], 'in': {'$not': '$$this'}}}");
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}
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@Test
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public void reduceTest() {
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// https://www.mongodb.com/docs/manual/reference/operator/aggregation/reduce/
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assertExpression(
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Stream.of(true, true, false)
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.reduce(false, (a, b) -> a || b),
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arrayTTF.reduce(of(false), (a, b) -> a.or(b)),
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// MQL:
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"{'$reduce': {'input': [true, true, false], 'initialValue': false, 'in': {'$or': ['$$this', '$$value']}}}");
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assertExpression(
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Stream.of(true, true, false)
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.reduce(true, (a, b) -> a && b),
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arrayTTF.reduce(of(true), (a, b) -> a.and(b)),
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// MQL:
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"{'$reduce': {'input': [true, true, false], 'initialValue': true, 'in': {'$and': ['$$this', '$$value']}}}");
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// empty array
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assertExpression(
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Stream.<Boolean>empty().reduce(true, (a, b) -> a && b),
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ofBooleanArray().reduce(of(true), (a, b) -> a.and(b)),
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// MQL:
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"{'$reduce': {'input': [], 'initialValue': true, 'in': {'$and': ['$$this', '$$value']}}}");
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// constant result
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assertExpression(
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Stream.of(true, true, false)
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.reduce(true, (a, b) -> true),
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arrayTTF.reduce(of(true), (a, b) -> of(true)),
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// MQL:
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"{'$reduce': {'input': [true, true, false], 'initialValue': true, 'in': true}}");
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}
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}

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