[ADT] Rewrite mapped_iterator in terms of iterator_adaptor_base.

Summary:
This eliminates the boilerplate implementation of the iterator interface in
mapped_iterator.

This patch also adds unit tests that verify that the mapped function is applied
by operator* and operator->, and that references returned by the map function
are returned via operator*.

Reviewers: dblaikie, chandlerc

Subscribers: llvm-commits, mgorny

Differential Revision: https://reviews.llvm.org/D39855

llvm-svn: 317902

2 files changed, 52 insertions, 0 deletions

diff --git a/llvm/unittests/ADT/CMakeLists.txt b/llvm/unittests/ADT/CMakeLists.txt
index d0313951dfa..e5b6bbf2a23 100644
--- a/llvm/unittests/ADT/CMakeLists.txt
+++ b/llvm/unittests/ADT/CMakeLists.txt
@@ -32,6 +32,7 @@ set(ADTSources
   IntrusiveRefCntPtrTest.cpp
   IteratorTest.cpp
   MakeUniqueTest.cpp
+  MappedIteratorTest.cpp
   MapVectorTest.cpp
   OptionalTest.cpp
   PackedVectorTest.cpp
diff --git a/llvm/unittests/ADT/MappedIteratorTest.cpp b/llvm/unittests/ADT/MappedIteratorTest.cpp
new file mode 100644
index 00000000000..d8c48a7d625
--- /dev/null
+++ b/llvm/unittests/ADT/MappedIteratorTest.cpp
@@ -0,0 +1,51 @@
+//===------ MappedIteratorTest.cpp - Unit tests for mapped_iterator -------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/STLExtras.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace {
+
+TEST(MappedIteratorTest, ApplyFunctionOnDereference) {
+  std::vector<int> V({0});
+
+  auto I = map_iterator(V.begin(), [](int X) { return X + 1; });
+
+  EXPECT_EQ(*I, 1) << "should have applied function in dereference";
+}
+
+TEST(MappedIteratorTest, ApplyFunctionOnArrow) {
+  struct S {
+    int Z = 0;
+  };
+
+  std::vector<int> V({0});
+  S Y;
+  S* P = &Y;
+
+  auto I = map_iterator(V.begin(), [&](int X) -> S& { return *(P + X); });
+
+  I->Z = 42;
+
+  EXPECT_EQ(Y.Z, 42) << "should have applied function during arrow";
+}
+
+TEST(MappedIteratorTest, FunctionPreservesReferences) {
+  std::vector<int> V({1});
+  std::map<int, int> M({ {1, 1} });
+
+  auto I = map_iterator(V.begin(), [&](int X) -> int& { return M[X]; });
+  *I = 42;
+
+  EXPECT_EQ(M[1], 42) << "assignment should have modified M";
+}
+
+} // anonymous namespace