Part 2 of base::IDMap refactor to eliminate IDMapOwnPointer/IDMapExternalPointer modes

base/id_map.h

Index: base/id_map.h
diff --git a/base/id_map.h b/base/id_map.h
index 74fb8d0b596cb7e1b0d758ad4e8ddfc3eb2b0103..9d67f1830e9c90a5159dad8d2edeb83b0b212bd0 100644
--- a/base/id_map.h
+++ b/base/id_map.h
@@ -17,18 +17,6 @@
 #include "base/macros.h"
 #include "base/sequence_checker.h"
 
-// Ownership semantics:
-// - OwnPointer means we store a unique_ptr that owns the object (so the
-//   object is deleted in Remove() and during destruction).
-// - ExternalPointer means we store a raw pointer and don't own the object
-
-// TODO (http://crbug.com/647091): eliminate this enum, replace OwnPointer
-// mode in callsites with IDMap<unique_ptr<T>>
-enum IDMapOwnershipSemantics {
-  IDMapExternalPointer,
-  IDMapOwnPointer
-};
-
 // This object maintains a list of IDs that can be quickly converted to
 // pointers to objects. It is implemented as a hash table, optimized for
 // relatively small data sets (in the common case, there will be exactly one
@@ -40,16 +28,13 @@ enum IDMapOwnershipSemantics {
 //
 // This class does not have a virtual destructor, do not inherit from it when

[danakj, 2016/11/30 23:02:21]

This comment doesn't quite make sense anymore. Does anything inherit from this?
That'd be crazy. Can you maybe just mark the class as final instead?

[rlanday, 2016/12/01 00:50:07]

Yeah it looks like nothing inherits from this

 // ownership semantics are set to own because pointers will leak.
-template <typename T,
-          IDMapOwnershipSemantics OS = IDMapExternalPointer,
-          typename K = int32_t>
+template <typename V, typename K = int32_t>

[danakj, 2016/11/30 23:02:21]

Maybe worth a comment now saying that the values (represented as the V
parameter) can be any type that can be dereferenced, such as a raw pointer or a
smart pointer.

[rlanday, 2016/12/01 00:50:07]

Ok, that's a good point

 class IDMap {
  public:
   using KeyType = K;
 
  private:
-  using V = typename std::
-      conditional<OS == IDMapExternalPointer, T*, std::unique_ptr<T>>::type;
+  using T = typename std::remove_reference<decltype(*V())>::type;
   using HashTable = base::hash_map<KeyType, V>;
 
  public:
@@ -149,9 +134,7 @@ class IDMap {
   template<class ReturnType>
   class Iterator {
    public:
-    Iterator(IDMap<T, OS, K>* map)
-        : map_(map),
-          iter_(map_->data_.begin()) {
+    Iterator(IDMap<V, K>* map) : map_(map), iter_(map_->data_.begin()) {
       Init();
     }
 
@@ -215,7 +198,7 @@ class IDMap {
       }
     }
 
-    IDMap<T, OS, K>* map_;
+    IDMap<V, K>* map_;
     typename HashTable::const_iterator iter_;
   };