[ADT] Add a generic iterator utility for adapting iterators much like

Boost's iterator_adaptor, and a specific adaptor which iterates over
pointees when wrapped around an iterator over pointers.

This is the result of a long discussion on IRC with Duncan Smith, Dave
Blaikie, Richard Smith, and myself. Essentially, I could use some subset
of the iterator facade facilities often used from Boost, and everyone
seemed interested in having the functionality in a reasonably generic
form. I've tried to strike a balance between the pragmatism and the
established Boost design. The primary differences are:

1) Delegating to the standard iterator interface names rather than
   special names that then make up a second iterator-like API.
2) Using the name 'pointee_iterator' which seems more clear than
   'indirect_iterator'. The whole business of calling the '*p' operation
   'pointer indirection' in the standard is ... quite confusing. And
   'dereference' is no better of a term for moving from a pointer to
   a reference.

Hoping Duncan, and others continue to provide comments on this until
we've got a nice, minimal abstraction.

llvm-svn: 207069

1 files changed, 59 insertions, 0 deletions

diff --git a/llvm/unittests/Support/IteratorTest.cpp b/llvm/unittests/Support/IteratorTest.cpp
new file mode 100644
index 0000000..3a16406
--- /dev/null
+++ b/llvm/unittests/Support/IteratorTest.cpp
@@ -0,0 +1,59 @@
+//===- IteratorTest.cpp - Unit tests for iterator utilities ---------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/iterator.h"
+#include "llvm/ADT/SmallVector.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace {
+
+TEST(PointeeIteratorTest, Basic) {
+  int arr[4] = { 1, 2, 3, 4 };
+  SmallVector<int *, 4> V;
+  V.push_back(&arr[0]);
+  V.push_back(&arr[1]);
+  V.push_back(&arr[2]);
+  V.push_back(&arr[3]);
+
+  typedef pointee_iterator<SmallVectorImpl<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