[optimise] Avoid unnecessary double iteration in fn:reverse

Author: adamretter

exist-core/pom.xml

@@ -1032,6 +1032,7 @@
                                 <include>src/main/java/org/exist/xquery/functions/fn/FunBaseURI.java</include>
                                 <include>src/main/java/org/exist/xquery/functions/fn/FunDeepEqual.java</include>
                                 <include>src/main/java/org/exist/xquery/functions/fn/FunParseIetfDate.java</include>
+                                <include>src/main/java/org/exist/xquery/functions/fn/FunReverse.java</include>
                                 <include>src/main/java/org/exist/xquery/functions/fn/FunSerialize.java</include>
                                 <include>src/main/java/org/exist/xquery/functions/fn/FunTrace.java</include>
                                 <include>src/main/java/org/exist/xquery/functions/fn/FunUnparsedText.java</include>
@@ -1466,6 +1467,7 @@
                                 <exclude>src/main/java/org/exist/xquery/functions/fn/FunDeepEqual.java</exclude>
                                 <exclude>src/main/java/org/exist/xquery/functions/fn/FunDocAvailable.java</exclude>
                                 <exclude>src/main/java/org/exist/xquery/functions/fn/FunParseIetfDate.java</exclude>
+                                <exclude>src/main/java/org/exist/xquery/functions/fn/FunReverse.java</exclude>
                                 <exclude>src/main/java/org/exist/xquery/functions/fn/FunSerialize.java</exclude>
                                 <exclude>src/main/java/org/exist/xquery/functions/fn/FunTrace.java</exclude>
                                 <exclude>src/main/java/org/exist/xquery/functions/fn/FunUnparsedText.java</exclude>

exist-core/src/main/java/org/exist/xquery/functions/fn/FunReverse.java

@@ -1,4 +1,28 @@
 /*
+ * Elemental
+ * Copyright (C) 2024, Evolved Binary Ltd
+ *
+ * [email protected]
+ * https://www.evolvedbinary.com | https://www.elemental.xyz
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; version 2.1.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * NOTE: Parts of this file contain code from 'The eXist-db Authors'.
+ *       The original license header is included below.
+ *
+ * =====================================================================
+ *
  * eXist-db Open Source Native XML Database
  * Copyright (C) 2001 The eXist-db Authors
  *
@@ -27,15 +51,15 @@
 import org.exist.xquery.value.FunctionReturnSequenceType;
 import org.exist.xquery.value.Item;
 import org.exist.xquery.value.Sequence;
-import org.exist.xquery.value.SequenceIterator;
+import org.exist.xquery.value.ValueSequence;
 import org.exist.xquery.value.SequenceType;
 import org.exist.xquery.value.Type;
-import org.exist.xquery.value.ValueSequence;
 
 /**
  * Implements the fn:reverse function.
  *
  * @author <a href="mailto:[email protected]">Piotr Kaminski</a>
+ * @author <a href="mailto:[email protected]">Adam Retter</a>
  */
 public class FunReverse extends Function {
 
@@ -79,37 +103,34 @@ public void analyze(final AnalyzeContextInfo contextInfo) throws XPathException
         argumentsChecked = true;
     }
 
-    public Sequence eval(Sequence contextSequence, Item contextItem) throws XPathException {
+    @Override
+    public Sequence eval(final Sequence contextSequence, final Item contextItem) throws XPathException {
         if (context.getProfiler().isEnabled()) {
-            context.getProfiler().start(this);       
+            context.getProfiler().start(this);
             context.getProfiler().message(this, Profiler.DEPENDENCIES, "DEPENDENCIES", Dependency.getDependenciesName(this.getDependencies()));
-            if (contextSequence != null)
-                {context.getProfiler().message(this, Profiler.START_SEQUENCES, "CONTEXT SEQUENCE", contextSequence);}
-            if (contextItem != null)
-                {context.getProfiler().message(this, Profiler.START_SEQUENCES, "CONTEXT ITEM", contextItem.toSequence());}
-        }           
-        
-        Sequence result;
+            if (contextSequence != null) {
+                context.getProfiler().message(this, Profiler.START_SEQUENCES, "CONTEXT SEQUENCE", contextSequence);
+            }
+            if (contextItem != null) {
+                context.getProfiler().message(this, Profiler.START_SEQUENCES, "CONTEXT ITEM", contextItem.toSequence());
+            }
+        }
+
         final Sequence seq = getArguments(contextSequence, contextItem)[0];
-		if (seq.isEmpty()) 
-            {result = Sequence.EMPTY_SEQUENCE;}
-        else {
-                final Sequence tmp = new ValueSequence();
-                Item item;
-                for(final SequenceIterator i = seq.iterate(); i.hasNext(); ) {
-                    item = i.nextItem();
-                    tmp.add(item);
-                }
-                result = new ValueSequence();
-                for (int i = seq.getItemCount() - 1; i >= 0; i--) {
-                    result.add(tmp.itemAt(i));
-                }
+        final Sequence result;
+        if (seq.isEmpty()) {
+            result = Sequence.EMPTY_SEQUENCE;
+        } else {
+            result = new ValueSequence();
+            for (int i = seq.getItemCount() - 1; i >= 0; i--) {
+                result.add(seq.itemAt(i));
+            }
         }
 
-        if (context.getProfiler().isEnabled()) 
-            {context.getProfiler().end(this, "", result);} 
-        
-        return result;
-	}
+        if (context.getProfiler().isEnabled()) {
+            context.getProfiler().end(this, "", result);
+        }
 
+        return result;
+    }
 }