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/*******************************************************************************
* Copyright (c) 2009 Cloudsmith Inc. and others.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* Cloudsmith Inc. - initial API and implementation
*******************************************************************************/
package org.eclipse.equinox.internal.p2.ql;
import java.util.*;
/**
* An expression that ensures that the elements of its collection is only returned
* once throughout the whole query.
*/
public final class Unique extends Binary {
public static class UniqueIterator extends MatchIteratorFilter {
private final Set uniqueSet;
public UniqueIterator(Class instanceClass, Iterator iterator, Set uniqueSet) {
super(instanceClass, iterator);
this.uniqueSet = uniqueSet;
}
protected boolean isMatch(Object val) {
synchronized (uniqueSet) {
return uniqueSet.add(val);
}
}
}
static final String OPERATOR = "unique"; //$NON-NLS-1$
public Unique(Expression collection, Expression cacheId) {
super(collection, cacheId);
}
public Object evaluate(ExpressionContext context, VariableScope scope) {
Object explicitCache = rhs.evaluate(context, scope);
Set uniqueSet;
if (explicitCache == null)
// No cache, we just ensure that the iteration is unique
uniqueSet = new HashSet();
else {
if (!(explicitCache instanceof Set))
throw new IllegalArgumentException("Unique cache must be a java.util.Set"); //$NON-NLS-1$
uniqueSet = (Set) explicitCache;
}
return new UniqueIterator(Object.class, lhs.evaluateAsIterator(context, scope), uniqueSet);
}
public void toString(StringBuffer bld) {
CollectionFilter.appendProlog(bld, lhs, getOperator());
if (rhs != Constant.NULL_CONSTANT)
appendOperand(bld, rhs, ExpressionParser.PRIORITY_COMMA);
bld.append(')');
}
String getOperator() {
return OPERATOR;
}
int getPriority() {
return ExpressionParser.PRIORITY_COLLECTION;
}
}
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