feature: Spoon Filter implements java.util.function.Predicate (#1798)

src/main/java/spoon/reflect/visitor/Filter.java

@@ -16,6 +16,8 @@
  */
 package spoon.reflect.visitor;
 
+import java.util.function.Predicate;
+
 import spoon.reflect.declaration.CtElement;
 
 /**
@@ -25,11 +27,15 @@
  * 		the type of the filtered elements (an element belonging to the
  * 		filtered element must be assignable from <code>T</code>).
  */
-public interface Filter<T extends CtElement> {
+public interface Filter<T extends CtElement> extends Predicate<T> {
 	/**
 	 * Tells if the given element matches.
 	 * @param element - the element to be checked for a match. Parameter element is never null if {@link Query} is used.
 	 */
 	boolean matches(T element);
 
+	@Override
+	default boolean test(T element) {
+		return matches(element);
+	}
 }

src/test/java/spoon/test/filters/FilterTest.java

@@ -4,6 +4,7 @@
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.fail;
@@ -14,12 +15,12 @@
 import java.util.Iterator;
 import java.util.List;
 import java.util.TreeSet;
+import java.util.function.Predicate;
 
 import org.junit.Before;
 import org.junit.Test;
 
 import spoon.Launcher;
-import spoon.SpoonException;
 import spoon.reflect.code.CtCFlowBreak;
 import spoon.reflect.code.CtExpression;
 import spoon.reflect.code.CtFieldAccess;
@@ -1284,4 +1285,13 @@ public void testNameFilterWithGenericType() {
 		assertEquals(1, ctFields.size());
 		assertTrue(ctFields.get(0) instanceof CtField);
 	}
+
+	@Test
+	public void testFilterAsPredicate() throws Exception {
+		CtClass<?> foo = factory.Package().get("spoon.test.filters").getType("Foo");
+		//contract: Spoon Filter is compatible with java.util.function.Predicate
+		Predicate predicate = new NamedElementFilter<>(CtClass.class, "Foo");
+		assertTrue(predicate.test(foo));
+		assertFalse(predicate.test(foo.getTypeMembers().get(0)));
+	}
 }