From 157d339906ff4b9fae59a04479e93022229ef778 Mon Sep 17 00:00:00 2001
From: Michael Bayne <mdb@samskivert.com>
Date: Thu, 20 Aug 2009 01:07:57 +0000
Subject: [PATCH] Provide a generic key element extraction higher-order
 function that works for any element type at any index.

---
 src/java/com/samskivert/depot/Key.java | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/src/java/com/samskivert/depot/Key.java b/src/java/com/samskivert/depot/Key.java
index 818ced6..7da1ba4 100644
--- a/src/java/com/samskivert/depot/Key.java
+++ b/src/java/com/samskivert/depot/Key.java
@@ -100,14 +100,25 @@ public class Key<T extends PersistentRecord> extends WhereClause
     }
 
     /**
-     * Extracts an integer key from a record's {@link Key}. This should only be used on records
-     * whose primary key is a single integer.
+     * Returns a function that extracts an integer from a record's {@link Key}. This should only be
+     * used on records whose primary key is a single integer.
      */
-    public static <T extends PersistentRecord> Function<Key<T>,Integer> toInt ()
+    public static <T extends PersistentRecord> Function<Key<T>, Integer> toInt ()
     {
-        return new Function<Key<T>,Integer>() {
-            public Integer apply (Key<T> key) {
-                return (Integer)key.getValues()[0];
+        return extract(0);
+    }
+
+    /**
+     * Returns a function that extracts an element key from a record's {@link Key}.
+     *
+     * @param index the index in the key of the element to be extracted.
+     */
+    public static <T extends PersistentRecord, E> Function<Key<T>, E> extract (final int index)
+    {
+        return new Function<Key<T>, E>() {
+            public E apply (Key<T> key) {
+                @SuppressWarnings("unchecked") E value = (E)key.getValues()[index];
+                return value;
             }
         };
     }