Index: src/java/org/apache/lucene/util/AttributeSource.java
===================================================================
--- src/java/org/apache/lucene/util/AttributeSource.java	(revision 922531)
+++ src/java/org/apache/lucene/util/AttributeSource.java	(working copy)
@@ -469,5 +469,24 @@
     
     return clone;
   }
+  
+  /**
+   * Copies the contents of this AttributeSource to the given target. This only works
+   * if the target uses the same {@link AttributeFactory} and contains at least the
+   * same {@link AttributeImpl}s this AttributeSource provides.
+   */
+  public final void copyTo(AttributeSource target) {
+    if (hasAttributes()) {
+      if (currentState == null) {
+        computeCurrentState();
+      }
+      for (State state = currentState; state != null; state = state.next) {
+        AttributeImpl targetImpl = target.attributeImpls.get(state.attribute.getClass());
+        if (targetImpl == null)
+          throw new IllegalArgumentException("This AttributeSource contains an AttributeImpl that is not in the target");
+        state.attribute.copyTo(targetImpl);
+      };
+    }
+  }
 
 }
Index: src/test/org/apache/lucene/util/TestAttributeSource.java
===================================================================
--- src/test/org/apache/lucene/util/TestAttributeSource.java	(revision 922531)
+++ src/test/org/apache/lucene/util/TestAttributeSource.java	(working copy)
@@ -95,6 +95,18 @@
     assertNotSame("TypeAttribute of original and clone must be different instances", typeAtt2, typeAtt);
     assertEquals("TermAttribute of original and clone must be equal", termAtt2, termAtt);
     assertEquals("TypeAttribute of original and clone must be equal", typeAtt2, typeAtt);
+    
+    // test copy back
+    termAtt2.setTermBuffer("OtherTerm");
+    typeAtt2.setType("OtherType");
+    clone.copyTo(src);
+    assertEquals("TermAttribute of original must now contain updated term", "OtherTerm", termAtt.term());
+    assertEquals("TypeAttribute of original must now contain updated type", "OtherType", typeAtt.type());
+    // verify again:
+    assertNotSame("TermAttribute of original and clone must be different instances", termAtt2, termAtt);
+    assertNotSame("TypeAttribute of original and clone must be different instances", typeAtt2, typeAtt);
+    assertEquals("TermAttribute of original and clone must be equal", termAtt2, termAtt);
+    assertEquals("TypeAttribute of original and clone must be equal", typeAtt2, typeAtt);
   }
   
   public void testToStringAndMultiAttributeImplementations() {