Clean up iterator typedefs.

This is a follow-up to
    https://android-review.googlesource.com/2736679 ,
    https://android-review.googlesource.com/2746156 .

Test: m
Bug: 175635923
Change-Id: Ia80fbea3b0570c6127fc0158cd43060b97a21ee7

3 files changed, 10 insertions, 7 deletions

diff --git a/libartbase/base/bit_vector.h b/libartbase/base/bit_vector.h
index a710c5d6ea..ea26b5a682 100644
--- a/libartbase/base/bit_vector.h
+++ b/libartbase/base/bit_vector.h
@@ -57,7 +57,7 @@ class BitVector {
     using value_type = uint32_t;
     using difference_type = ptrdiff_t;
     using pointer = void;
-    using reference = uint32_t;
+    using reference = void;
 
     bool operator==(const IndexIterator& other) const;
 
diff --git a/libartbase/base/stl_util.h b/libartbase/base/stl_util.h
index 87b6d4bf3e..53eb410519 100644
--- a/libartbase/base/stl_util.h
+++ b/libartbase/base/stl_util.h
@@ -195,8 +195,8 @@ class CountIter {
   using iterator_category = std::forward_iterator_tag;
   using value_type = size_t;
   using difference_type = size_t;
-  using pointer = size_t;
-  using reference = size_t;
+  using pointer = void;
+  using reference = void;
 
   CountIter() : count_(0) {}
   explicit CountIter(size_t count) : count_(count) {}
@@ -251,10 +251,10 @@ template <typename RealIter, typename Filter>
 struct FilterIterator {
  public:
   using iterator_category = std::forward_iterator_tag;
-  using value_type = typename RealIter::value_type;
+  using value_type = typename std::iterator_traits<RealIter>::value_type;
   using difference_type = ptrdiff_t;
-  using pointer = typename RealIter::pointer;
-  using reference = typename RealIter::reference;
+  using pointer = typename std::iterator_traits<RealIter>::pointer;
+  using reference = typename std::iterator_traits<RealIter>::reference;
 
   FilterIterator(RealIter rl,
                  Filter cond,
diff --git a/libartbase/base/transform_iterator.h b/libartbase/base/transform_iterator.h
index 552f31fa3b..3f7c952b60 100644
--- a/libartbase/base/transform_iterator.h
+++ b/libartbase/base/transform_iterator.h
@@ -43,7 +43,10 @@ class TransformIterator {
                                   typename std::iterator_traits<BaseIterator>::iterator_category>,
                 "Transform iterator base must be an input iterator.");
 
-  using InputType = typename std::iterator_traits<BaseIterator>::reference;
+  using BaseReference = typename std::iterator_traits<BaseIterator>::reference;
+  using InputType = std::conditional_t<std::is_same_v<BaseReference, void>,
+                                       typename std::iterator_traits<BaseIterator>::value_type,
+                                       BaseReference>;
   using ResultType = std::result_of_t<Function(InputType)>;
 
  public: