Move prependToList to ListValue and remove copying

community/collections/src/main/java/org/neo4j/helpers/collection/Iterators.java

@@ -122,7 +122,7 @@ public static <T> T last( Iterator<T> iterator )
      * Returns the given iterator's single element or {@code null} if no
      * element found. If there is more than one element in the iterator a
      * {@link NoSuchElementException} will be thrown.
-     *
+     * <p>
      * If the {@code iterator} implements {@link Resource} it will be {@link Resource#close() closed}
      * in a {@code finally} block after the single item has been retrieved, or failed to be retrieved.
      *
@@ -141,7 +141,7 @@ public static <T> T singleOrNull( Iterator<T> iterator )
      * Returns the given iterator's single element. If there are no elements
      * or more than one element in the iterator a {@link NoSuchElementException}
      * will be thrown.
-     *
+     * <p>
      * If the {@code iterator} implements {@link Resource} it will be {@link Resource#close() closed}
      * in a {@code finally} block after the single item has been retrieved, or failed to be retrieved.
      *
@@ -234,7 +234,7 @@ private static <T> T assertNotNull( Iterator<T> iterator, T result )
      * Returns the given iterator's single element or {@code itemIfNone} if no
      * element found. If there is more than one element in the iterator a
      * {@link NoSuchElementException} will be thrown.
-     *
+     * <p>
      * If the {@code iterator} implements {@link Resource} it will be {@link Resource#close() closed}
      * in a {@code finally} block after the single item has been retrieved, or failed to be retrieved.
      *
@@ -253,7 +253,7 @@ public static <T> T single( Iterator<T> iterator, T itemIfNone )
             if ( iterator.hasNext() )
             {
                 throw new NoSuchElementException( "More than one element in " + iterator + ". First element is '"
-                        + result + "' and the second element is '" + iterator.next() + "'" );
+                                                  + result + "' and the second element is '" + iterator.next() + "'" );
             }
             return result;
         }
@@ -268,14 +268,15 @@ public static <T> T single( Iterator<T> iterator, T itemIfNone )
 
     /**
      * Adds all the items in {@code iterator} to {@code collection}.
+     *
      * @param <C> the type of {@link Collection} to add to items to.
      * @param <T> the type of items in the collection and iterator.
      * @param iterator the {@link Iterator} to grab the items from.
      * @param collection the {@link Collection} to add the items to.
      * @return the {@code collection} which was passed in, now filled
      * with the items from {@code iterator}.
      */
-    public static <C extends Collection<T>,T> C addToCollection( Iterator<T> iterator,
+    public static <C extends Collection<T>, T> C addToCollection( Iterator<T> iterator,
             C collection )
     {
         while ( iterator.hasNext() )
@@ -287,14 +288,15 @@ public static <C extends Collection<T>,T> C addToCollection( Iterator<T> iterato
 
     /**
      * Adds all the items in {@code iterator} to {@code collection}.
+     *
      * @param <C> the type of {@link Collection} to add to items to.
      * @param <T> the type of items in the collection and iterator.
      * @param iterator the {@link Iterator} to grab the items from.
      * @param collection the {@link Collection} to add the items to.
      * @return the {@code collection} which was passed in, now filled
      * with the items from {@code iterator}.
      */
-    public static <C extends Collection<T>,T> C addToCollectionUnique( Iterator<T> iterator,
+    public static <C extends Collection<T>, T> C addToCollectionUnique( Iterator<T> iterator,
             C collection )
     {
         while ( iterator.hasNext() )
@@ -309,20 +311,21 @@ private static <T, C extends Collection<T>> void addUnique( C collection, T item
         if ( !collection.add( item ) )
         {
             throw new IllegalStateException( "Encountered an already added item:" + item +
-                    " when adding items uniquely to a collection:" + collection );
+                                             " when adding items uniquely to a collection:" + collection );
         }
     }
 
     /**
      * Adds all the items in {@code iterator} to {@code collection}.
+     *
      * @param <C> the type of {@link Collection} to add to items to.
      * @param <T> the type of items in the collection and iterator.
      * @param iterable the {@link Iterator} to grab the items from.
      * @param collection the {@link Collection} to add the items to.
      * @return the {@code collection} which was passed in, now filled
      * with the items from {@code iterator}.
      */
-    public static <C extends Collection<T>,T> C addToCollectionUnique( Iterable<T> iterable,
+    public static <C extends Collection<T>, T> C addToCollectionUnique( Iterable<T> iterable,
             C collection )
     {
         return addToCollectionUnique( iterable.iterator(), collection );
@@ -371,6 +374,7 @@ public static <T> long count( Iterator<T> iterator )
     /**
      * Counts the number of filtered in the {@code iterator} by looping
      * through it.
+     *
      * @param <T> the type of items in the iterator.
      * @param iterator the {@link Iterator} to count items in.
      * @param filter the filter to test items against
@@ -399,7 +403,7 @@ public static <T> List<T> asList( Iterator<T> iterator )
         return addToCollection( iterator, new ArrayList<>() );
     }
 
-    public static <T, EX extends Exception> List<T> asList( RawIterator<T, EX> iterator ) throws EX
+    public static <T, EX extends Exception> List<T> asList( RawIterator<T,EX> iterator ) throws EX
     {
         List<T> out = new ArrayList<>();
         while ( iterator.hasNext() )
@@ -577,13 +581,13 @@ public void remove()
     }
 
     @SafeVarargs
-    public static <T> Iterator<T> iterator( T ... items )
+    public static <T> Iterator<T> iterator( T... items )
     {
         return asIterator( items.length, items );
     }
 
     @SafeVarargs
-    public static <T> Iterator<T> iterator( int maxItems, T ... items )
+    public static <T> Iterator<T> iterator( int maxItems, T... items )
     {
         return asIterator( maxItems, items );
     }
@@ -619,6 +623,37 @@ else if ( index < appended.length )
         };
     }
 
+    public static <T> Iterator<T> prependTo( Iterator<T> iterator, T... prepended )
+    {
+        return new Iterator<T>()
+        {
+            private int index;
+
+            @Override
+            public boolean hasNext()
+            {
+                return index < prepended.length || iterator.hasNext();
+            }
+
+            @Override
+            public T next()
+            {
+                if ( index < prepended.length )
+                {
+                    return prepended[index++];
+                }
+                else if ( iterator.hasNext() )
+                {
+                    return iterator.next();
+                }
+                else
+                {
+                    throw new NoSuchElementException();
+                }
+            }
+        };
+    }
+
     @SuppressWarnings( "unchecked" )
     public static <T> ResourceIterator<T> emptyResourceIterator()
     {
@@ -685,18 +720,18 @@ public static <X> Iterator<X> filter( Predicate<? super X> specification, Iterat
         return new FilterIterable.FilterIterator<>( i, specification );
     }
 
-    public static <FROM, TO> Iterator<TO> map( Function<? super FROM, ? extends TO> function, Iterator<FROM> from )
+    public static <FROM, TO> Iterator<TO> map( Function<? super FROM,? extends TO> function, Iterator<FROM> from )
     {
         return new MapIterable.MapIterator<>( from, function );
     }
 
-    public static <FROM, TO, EX extends Exception> RawIterator<TO, EX> map(
-            ThrowingFunction<? super FROM, ? extends TO, EX> function, RawIterator<FROM, EX> from )
+    public static <FROM, TO, EX extends Exception> RawIterator<TO,EX> map(
+            ThrowingFunction<? super FROM,? extends TO,EX> function, RawIterator<FROM,EX> from )
     {
         return new RawMapIterator<>( from, function );
     }
 
-    public static <T, EX extends Exception> RawIterator<T, EX> asRawIterator( Iterator<T> iter )
+    public static <T, EX extends Exception> RawIterator<T,EX> asRawIterator( Iterator<T> iter )
     {
         return new RawIterator<T,EX>()
         {
@@ -714,14 +749,15 @@ public T next()
         };
     }
 
-    public static <T, EX extends Exception> RawIterator<T, EX> asRawIterator( Stream<T> stream )
+    public static <T, EX extends Exception> RawIterator<T,EX> asRawIterator( Stream<T> stream )
     {
         return asRawIterator( stream.iterator() );
     }
 
-    public static <FROM, TO> Iterator<TO> flatMap( Function<? super FROM, ? extends Iterator<TO>> function, Iterator<FROM> from )
+    public static <FROM, TO> Iterator<TO> flatMap( Function<? super FROM,? extends Iterator<TO>> function,
+            Iterator<FROM> from )
     {
-        return new CombiningIterator<>( map(function, from) );
+        return new CombiningIterator<>( map( function, from ) );
     }
 
     @SafeVarargs
@@ -775,7 +811,7 @@ protected T fetchNextOrNull()
 
     /**
      * Create a stream from the given iterator.
-     * <p>
+     *
      * <b>Note:</b> returned stream needs to be closed via {@link Stream#close()} if the given iterator implements
      * {@link Resource}.
      *
@@ -791,7 +827,7 @@ public static <T> Stream<T> stream( Iterator<T> iterator )
 
     /**
      * Create a stream from the given iterator with given characteristics.
-     * <p>
+     *
      * <b>Note:</b> returned stream needs to be closed via {@link Stream#close()} if the given iterator implements
      * {@link Resource}.
      *

community/cypher/cypher/src/main/java/org/neo4j/cypher/internal/codegen/CompiledMathHelper.java

@@ -93,11 +93,11 @@ else if ( rhs instanceof ListValue )
             }
             else if ( lhs instanceof AnyValue )
             {
-                return VirtualValues.prependToList( (ListValue) rhs, (AnyValue) lhs );
+                return ( (ListValue) rhs).prepend( (AnyValue) lhs );
             }
             else
             {
-                return VirtualValues.prependToList( (ListValue) rhs, ValueUtils.of( lhs ) );
+                return ((ListValue) rhs).prepend( ValueUtils.of( lhs ) );
             }
         }
         else if ( lhs instanceof List<?> && rhs instanceof List<?> )

community/cypher/interpreted-runtime/src/main/scala/org/neo4j/cypher/internal/runtime/interpreted/commands/expressions/Add.scala

@@ -40,7 +40,7 @@ case class Add(a: Expression, b: Expression) extends Expression {
       case (x: TextValue, y: TextValue) => Values.stringValue(x.stringValue() + y.stringValue())
       case (IsList(x), IsList(y)) => VirtualValues.concat(x, y)
       case (IsList(x), y)         => x.append(y)
-      case (x, IsList(y))         => VirtualValues.prependToList(y, x)
+      case (x, IsList(y))         => y.prepend(x)
       case (x: TextValue, y: IntegralValue) => Values.stringValue(x.stringValue() + y.longValue())
       case (x: IntegralValue, y: TextValue) => Values.stringValue(x.longValue() + y.stringValue())
       case (x: TextValue, y: FloatValue) => Values.stringValue(x.stringValue() + y.doubleValue())
@@ -57,11 +57,5 @@ case class Add(a: Expression, b: Expression) extends Expression {
 
   def arguments = Seq(a, b)
 
-  private def mergeWithCollection(collection: CypherType, singleElement: CypherType):CypherType= {
-    val collectionType = collection.asInstanceOf[ListType]
-    val mergedInnerType = collectionType.innerType.leastUpperBound(singleElement)
-    CTList(mergedInnerType)
-  }
-
   def symbolTableDependencies = a.symbolTableDependencies ++ b.symbolTableDependencies
 }

community/values/src/main/java/org/neo4j/values/virtual/ListValue.java

@@ -556,7 +556,7 @@ public AnyValue value( int offset )
             {
                 return base.value( offset );
             }
-            else if ( offset < size + appended.length)
+            else if ( offset < size + appended.length )
             {
                 return appended[offset - size];
             }
@@ -581,6 +581,62 @@ public Iterator<AnyValue> iterator()
         }
     }
 
+    static final class PrependList extends ListValue
+    {
+        private final ListValue base;
+        private final AnyValue[] prepended;
+
+        PrependList( ListValue base, AnyValue[] prepended )
+        {
+            this.base = base;
+            this.prepended = prepended;
+        }
+
+        @Override
+        public IterationPreference iterationPreference()
+        {
+            return base.iterationPreference();
+        }
+
+        @Override
+        public int size()
+        {
+            return prepended.length + base.size();
+        }
+
+        @Override
+        public AnyValue value( int offset )
+        {
+            int size = base.size();
+            if ( offset < prepended.length )
+            {
+                return prepended[offset];
+            }
+            else if ( offset < size + prepended.length )
+            {
+                return base.value( offset - size );
+            }
+            else
+            {
+                throw new IndexOutOfBoundsException( offset + " is outside range " + size );
+            }
+        }
+
+        @Override
+        public Iterator<AnyValue> iterator()
+        {
+            switch ( base.iterationPreference() )
+            {
+            case RANDOM_ACCESS:
+                return super.iterator();
+            case ITERATION:
+                return Iterators.prependTo( base.iterator(), prepended );
+            default:
+                throw new IllegalStateException( "unknown iteration preference" );
+            }
+        }
+    }
+
     public boolean isEmpty()
     {
         return size() == 0;
@@ -793,9 +849,22 @@ public ListValue reverse()
         return new ReversedList( this );
     }
 
-    public ListValue append( AnyValue...value )
+    public ListValue append( AnyValue...values )
     {
-        return new AppendList( this, value );
+        if ( values.length == 0 )
+        {
+            return this;
+        }
+        return new AppendList( this, values );
+    }
+
+    public ListValue prepend( AnyValue...values )
+    {
+        if ( values.length == 0 )
+        {
+            return this;
+        }
+        return new PrependList( this, values );
     }
 
     private AnyValue[] iterationAsArray()

community/values/src/main/java/org/neo4j/values/virtual/VirtualValues.java

@@ -80,14 +80,6 @@ public static ListValue concat( ListValue... lists )
         return new ListValue.ConcatList( lists );
     }
 
-    public static ListValue prependToList( ListValue list, AnyValue value )
-    {
-        AnyValue[] newValues = new AnyValue[list.size() + 1];
-        newValues[0] = value;
-        System.arraycopy( list.asArray(), 0, newValues, 1, list.size() );
-        return VirtualValues.list( newValues );
-    }
-
     public static MapValue emptyMap()
     {
         return EMPTY_MAP;