[ADT] Generalize pointee_iterator to smart pointers by using decltype.

Based on review feedback from Dave on the original patch.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207146 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/iterator.h

@@ -163,10 +163,9 @@ public:
 /// \code
 ///   typedef pointee_iterator<SmallVectorImpl<T *>::iterator> iterator;
 /// \endcode
-template <
+template <typename WrappedIteratorT,
-    typename WrappedIteratorT,
+          typename T = typename std::remove_reference<
-    typename T = typename std::remove_pointer<
+              decltype(**std::declval<WrappedIteratorT>())>::type>
-        typename std::iterator_traits<WrappedIteratorT>::value_type>::type>
 struct pointee_iterator
     : iterator_adaptor_base<pointee_iterator<WrappedIteratorT>,
                             WrappedIteratorT, T> {

unittests/Support/IteratorTest.cpp

@@ -8,6 +8,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ADT/iterator.h"
+#include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallVector.h"
 #include "gtest/gtest.h"
 
@@ -56,4 +57,45 @@ TEST(PointeeIteratorTest, Basic) {
   EXPECT_EQ(End, I);
 }
 
+TEST(PointeeIteratorTest, SmartPointer) {
+  SmallVector<std::unique_ptr<int>, 4> V;
+  V.push_back(make_unique<int>(1));
+  V.push_back(make_unique<int>(2));
+  V.push_back(make_unique<int>(3));
+  V.push_back(make_unique<int>(4));
+
+  typedef pointee_iterator<
+      SmallVectorImpl<std::unique_ptr<int>>::const_iterator> test_iterator;
+
+  test_iterator Begin, End;
+  Begin = V.begin();
+  End = test_iterator(V.end());
+
+  test_iterator I = Begin;
+  for (int i = 0; i < 4; ++i) {
+    EXPECT_EQ(*V[i], *I);
+
+    EXPECT_EQ(I, Begin + i);
+    EXPECT_EQ(I, std::next(Begin, i));
+    test_iterator J = Begin;
+    J += i;
+    EXPECT_EQ(I, J);
+    EXPECT_EQ(*V[i], Begin[i]);
+
+    EXPECT_NE(I, End);
+    EXPECT_GT(End, I);
+    EXPECT_LT(I, End);
+    EXPECT_GE(I, Begin);
+    EXPECT_LE(Begin, I);
+
+    EXPECT_EQ(i, I - Begin);
+    EXPECT_EQ(i, std::distance(Begin, I));
+    EXPECT_EQ(Begin, I - i);
+
+    test_iterator K = I++;
+    EXPECT_EQ(K, std::prev(I));
+  }
+  EXPECT_EQ(End, I);
+}
+
 } // anonymous namespace