First attempt at providing default traits for PersistentValueMap.

include/v8-util.h

Index: include/v8-util.h
diff --git a/include/v8-util.h b/include/v8-util.h
index 5cee46704af332d97443c903b59f92384e7f490c..eb06b56002aa15bc829558cb480f34d153aac692 100644
--- a/include/v8-util.h
+++ b/include/v8-util.h
@@ -42,6 +42,69 @@ namespace v8 {
 typedef uintptr_t PersistentContainerValue;
 static const uintptr_t kPersistentContainerNotFound = 0;
 
+
+namespace persistent_value_map_traits {

[dcarney, 2014/03/17 12:53:55]

no need for a new namespace

[vogelheim, 2014/03/17 19:20:37]

Removed.

+
+template<typename K, typename V>
+class WeakSTLMapTraits {

[dcarney, 2014/03/17 12:53:55]

would be better as StdPersistentValueMap  which itself has weak traits, which
default to something which does nothing

[vogelheim, 2014/03/17 19:20:37]

I couldn't really figure this one out. What I've done now is:

- Fixed the K() issue, so that the (optional) Traits methods with return values
can always be implemented as 'return NULL'.
- Renamed the Traits class to be more consistent with its actual role:
DefaultSTLMapTraits.

The test-api.cc demonstrates how to use the traits class as-is, and how to
implement a map w/ weak callbacks by deriving a custom traits class from the
default one.

Let's briefly discuss whether that addresses your concerns.

+ public:
+  // STL map & related:
+  typedef std::map<K, v8::PersistentContainerValue> Impl;
+  typedef typename Impl::iterator Iterator;
+
+  static bool Empty(Impl* impl) { return impl->empty(); }
+  static size_t Size(Impl* impl) { return impl->size(); }
+  static void Swap(Impl& a, Impl& b) { std::swap(a, b); }  // NOLINT
+  static Iterator Begin(Impl* impl) { return impl->begin(); }
+  static Iterator End(Impl* impl) { return impl->end(); }
+  static K Key(Iterator it) { return it->first; }
+  static v8::PersistentContainerValue Value(Iterator it) { return it->second; }
+  static v8::PersistentContainerValue Set(Impl* impl, K key,
+      v8::PersistentContainerValue value) {
+    std::pair<Iterator, bool> res = impl->insert(std::make_pair(key, value));
+    v8::PersistentContainerValue old_value = v8::kPersistentContainerNotFound;
+    if (!res.second) {
+      old_value = res.first->second;
+      res.first->second = value;
+    }
+    return old_value;
+  }
+  static v8::PersistentContainerValue Get(Impl* impl, K key) {
+    Iterator it = impl->find(key);
+    if (it == impl->end()) return v8::kPersistentContainerNotFound;
+    return it->second;
+  }
+  static v8::PersistentContainerValue Remove(Impl* impl, K key) {
+    Iterator it = impl->find(key);
+    if (it == impl->end()) return v8::kPersistentContainerNotFound;
+    v8::PersistentContainerValue value = it->second;
+    impl->erase(it);
+    return value;
+  }
+
+  // Weak callback & friends:
+  static const bool kIsWeak = false;

[dcarney, 2014/03/17 12:53:55]

this should be true for a class called WeakSTLMapTraits

[vogelheim, 2014/03/17 19:20:37]

Yes. But actually, this class was misnamed, since it didn't actually implement a
'weak' maps trait. So I renamed the class instead.

+  typedef void WeakCallbackDataType;
+  static void Dispose(v8::Isolate* isolate, v8::UniquePersistent<V> value,
+      Impl* impl, K key) {}
+  static WeakCallbackDataType* WeakCallbackParameter(Impl* impl, const K& key,
+      Local<V> value) {
+    return NULL;
+  }
+  static Impl* ImplFromWeakCallbackData(
+      const v8::WeakCallbackData<V, WeakCallbackDataType>& data) {
+    return NULL;
+  }
+  static K KeyFromWeakCallbackData(
+      const v8::WeakCallbackData<V, WeakCallbackDataType>& data) {
+    return K();
+  }
+  static void DisposeCallbackData(WeakCallbackDataType* data) {
+  }
+};
+
+}  // namespace persistent_value_map_traits
+
 /**
  * A map wrapper that allows using UniquePersistent as a mapped value.
  * C++11 embedders don't need this class, as they can use UniquePersistent