added MustacheCustomContext

src/main/java/com/samskivert/mustache/BasicCollector.java

@@ -35,6 +35,7 @@ public abstract class BasicCollector implements Mustache.Collector
     }
 
     public Mustache.VariableFetcher createFetcher (Object ctx, String name) {
+        if (ctx instanceof MustacheCustomContext) return CUSTOM_FETCHER;
         if (ctx instanceof Map<?,?>) return MAP_FETCHER;
 
         // if the name looks like a number, potentially use one of our 'indexing' fetchers
@@ -65,6 +66,17 @@ public abstract class BasicCollector implements Mustache.Collector
         return null;
     }
 
+    protected static final Mustache.VariableFetcher CUSTOM_FETCHER = new Mustache.VariableFetcher() {
+        public Object get (Object ctx, String name) throws Exception {
+            MustacheCustomContext custom = (MustacheCustomContext)ctx;
+            Object val = custom.get(name);
+            return val == null ? Template.NO_FETCHER_FOUND : val;
+        }
+        @Override public String toString () {
+            return "CUSTOM_FETCHER";
+        }
+    };
+
     protected static final Mustache.VariableFetcher MAP_FETCHER = new Mustache.VariableFetcher() {
         public Object get (Object ctx, String name) throws Exception {
             Map<?,?> map = (Map<?,?>)ctx;

src/main/java/com/samskivert/mustache/MustacheCustomContext.java

@@ -0,0 +1,8 @@
+package com.samskivert.mustache;
+
+/**
+ * Provides a simple interface for callers to implement their own logic for contextual values.
+ */
+public interface MustacheCustomContext {
+    Object get(String name) throws Exception;
+}