XList is going away. To be replaced with this, still somewhat out of place in a

database library but at least slightly more ignorable, bit of functional
helpfulness.

src/java/com/samskivert/depot/DepotRepository.java

@@ -31,19 +31,21 @@ import java.util.List;
 import java.util.Map;
 import java.util.Set;
 
+import com.google.common.base.Function;
 import com.google.common.collect.Lists;
 import com.google.common.collect.Sets;
 
 import com.samskivert.util.ArrayUtil;
 
-import com.samskivert.jdbc.ConnectionProvider;
-import com.samskivert.jdbc.DatabaseLiaison;
 import com.samskivert.depot.clause.FieldOverride;
 import com.samskivert.depot.clause.InsertClause;
 import com.samskivert.depot.clause.QueryClause;
 import com.samskivert.depot.clause.WhereClause;
 import com.samskivert.depot.expression.ColumnExp;
 import com.samskivert.depot.expression.SQLExpression;
+import com.samskivert.depot.util.Sequence;
+import com.samskivert.jdbc.ConnectionProvider;
+import com.samskivert.jdbc.DatabaseLiaison;
 
 import com.samskivert.depot.impl.DepotMarshaller;
 import com.samskivert.depot.impl.DepotMigrationHistoryRecord;
@@ -905,6 +907,14 @@ public abstract class DepotRepository
         return (value instanceof SQLExpression) ? (SQLExpression)value : new ValueExp(value);
     }
 
+    /**
+     * Concise way to call {@link Sequence#map} to transform query results.
+     */
+    protected <F, T> Sequence<T> map (Collection<F> source, Function<? super F, ? extends T> func)
+    {
+        return Sequence.map(source, func);
+    }
+
     protected PersistenceContext _ctx;
     protected List<DataMigration> _dataMigs = Lists.newArrayList();
 }

src/java/com/samskivert/depot/util/Sequence.java

@@ -0,0 +1,83 @@
+//
+// $Id$
+//
+// Depot library - a Java relational persistence library
+// Copyright (C) 2006-2009 Michael Bayne and Pär Winzell
+//
+// 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; either version 2.1 of the License, or
+// (at your option) any later version.
+//
+// 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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+
+package com.samskivert.depot.util;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Iterator;
+
+import com.google.common.base.Function;
+import com.google.common.collect.Iterators;
+
+/**
+ * Provides read-only access to a sequence of elements. Note that these elements will generally be
+ * computed via the application of a {@link Function} *every time* you iterate over this sequence.
+ * Thus a caller is expected to either simply iterate over the elements once, or use {@link
+ * #toList} to convert the sequence to concrete list to avoid repeated application of the
+ * conversion function on elements of the sequence.
+ */
+public abstract class Sequence<T> implements Iterable<T>
+{
+    /**
+     * Applies the supplied mapping function to the elements in the supplied collection, returning
+     * a lazily created read-only view of the mapped elements.
+     */
+    public static <F, T> Sequence<T> map (final Collection<F> source,
+                                          final Function<? super F, ? extends T> func)
+    {
+        return new Sequence<T>() {
+            public Iterator<T> iterator () {
+                return Iterators.transform(source.iterator(), func);
+            }
+            public int size () {
+                return source.size();
+            }
+            public boolean isEmpty () {
+                return source.isEmpty();
+            }
+            public ArrayList<T> toList () {
+                ArrayList<T> list = new ArrayList<T>(source.size());
+                for (F elem : source) {
+                    list.add(func.apply(elem));
+                }
+                return list;
+            }
+        };
+    }
+
+    // from interface Iterable
+    public abstract Iterator<T> iterator ();
+
+    /**
+     * Returns the number of elements in this sequence.
+     */
+    public abstract int size ();
+
+    /**
+     * Returns true if this sequence is empty, false if it contains at least one element.
+     */
+    public abstract boolean isEmpty ();
+
+    /**
+     * Converts this sequence into an array list.
+     */
+    public abstract ArrayList<T> toList ();
+}