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diff --git a/bundles/org.eclipse.equinox.p2.metadata/src/org/eclipse/equinox/p2/metadata/expression/IMatchExpression.java b/bundles/org.eclipse.equinox.p2.metadata/src/org/eclipse/equinox/p2/metadata/expression/IMatchExpression.java
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+++ b/bundles/org.eclipse.equinox.p2.metadata/src/org/eclipse/equinox/p2/metadata/expression/IMatchExpression.java
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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.p2.metadata.expression;
+
+/**
+ * A match expression is a boolean expression matching a candidate of a
+ * specific type. An {@link IEvaluationContext} is needed in order to evaluate
+ * a match and this class provides two ways of doing that. Either a context
+ * is created first and then reused in several subsequent calls to
+ * {@link #isMatch(IEvaluationContext, Object)} or, if no repeated calls are
+ * expected, the {@link #isMatch(Object)} method can be used. It will then
+ * create a context on each call.
+ */
+public interface IMatchExpression<T> extends IExpression {
+	/**
+	 * <p>Creates a new context to be passed to repeated subsequent evaluations. The context
+	 * will introduce 'this' as an uninitialized variable and make the parameters available.
+	 * @return A new evaluation context.
+	 */
+	IEvaluationContext createContext();
+
+	/**
+	 * Returns the parameters that this match expression was created with.
+	 * @return An array of parameters, possibly empty but never <code>null</code>.
+	 */
+	Object[] getParameters();
+
+	/**
+	 * This method creates a new evaluation context and assigns the <code>candidate</code>
+	 * to the 'this' variable of the <code>context</code> and then evaluates the expression.
+	 * This is essentially a short form for <pre>isMatch(createContext(), candidate)</pre>.
+	 * @param candidate The object to test.
+	 * @return the result of the evaluation.
+	 */
+	boolean isMatch(T candidate);
+
+	/**
+	 * This method assigns <code>candidate</code> to the 'this' variable of the
+	 * <code>context</code> and then evaluates the expression.
+	 * @param context A context
+	 * @param candidate The object to test.
+	 * @return the result of the evaluation.
+	 */
+	boolean isMatch(IEvaluationContext context, T candidate);
+}