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/*******************************************************************************
* Copyright (c) 2009, 2010 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.metadata.expression;
import java.util.*;
import org.eclipse.equinox.p2.metadata.expression.IEvaluationContext;
/**
* An expression that ensures that the elements of its collection is only returned
* once throughout the whole query.
*/
final class Unique extends Binary {
/**
* A UniqueIterator that uses a set as a discriminator, ensuring that
* no element is returned twice.
*/
static class UniqueIterator<T> extends MatchIteratorFilter<T> {
final Set<T> uniqueSet;
public UniqueIterator(Iterator<? extends T> iterator, Set<T> uniqueSet) {
super(iterator);
this.uniqueSet = uniqueSet;
}
protected boolean isMatch(T val) {
synchronized (uniqueSet) {
return uniqueSet.add(val);
}
}
}
Unique(Expression collection, Expression explicitCache) {
super(collection, explicitCache);
}
public Object evaluate(IEvaluationContext context) {
return evaluateAsIterator(context);
}
@SuppressWarnings("unchecked")
public Iterator<?> evaluateAsIterator(IEvaluationContext context) {
Object explicitCache = rhs.evaluate(context);
Set<Object> uniqueSet;
if (explicitCache == null)
// No cache, we just ensure that the iteration is unique
uniqueSet = new HashSet<Object>();
else {
if (!(explicitCache instanceof Set<?>))
throw new IllegalArgumentException("Unique cache must be a java.util.Set"); //$NON-NLS-1$
uniqueSet = (Set<Object>) explicitCache;
}
return new UniqueIterator<Object>(lhs.evaluateAsIterator(context), uniqueSet);
}
public int getExpressionType() {
return TYPE_UNIQUE;
}
public void toString(StringBuffer bld, Variable rootVariable) {
CollectionFilter.appendProlog(bld, rootVariable, lhs, getOperator());
if (rhs != Literal.NULL_CONSTANT)
appendOperand(bld, rootVariable, rhs, IExpressionConstants.PRIORITY_COMMA);
bld.append(')');
}
public String getOperator() {
return KEYWORD_UNIQUE;
}
public int getPriority() {
return PRIORITY_COLLECTION;
}
}
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