[ADT] drop_begin: use adl_begin/adl_end. NFC.

Meinersbur · Meinersbur · commit 2cb219994868 · 2018-06-27T19:39:03.000Z
Summary: The instantiation of the drop_begin function template usually fails because the functions begin() and end() do not exist. Only when using on a container from the std namespace (or `llvm::iterator_range`s of something derived from `std::iterator`), they are matched to std::begin() and std::end() due to Koenig-lookup. Explicitly use llvm::adl_begin and llvm::adl_end to make drop_begin applicable to anything iterable (including C-style arrays). A solution for general `llvm::iterator_range`s was already tried in r244620, but got reverted in r244621 due to MSVC not liking it. Reviewers: dblaikie, grosbach, aaron.ballman, ruiu Reviewed By: dblaikie, aaron.ballman Subscribers: aaron.ballman, llvm-commits Differential Revision: https://reviews.llvm.org/D48598 llvm-svn: 335772
diff --git a/llvm/include/llvm/ADT/iterator_range.h b/llvm/include/llvm/ADT/iterator_range.h
@@ -59,9 +59,10 @@ template <typename T> iterator_range<T> make_range(std::pair<T, T> p) {
   return iterator_range<T>(std::move(p.first), std::move(p.second));
 }
 
-template<typename T>
-iterator_range<decltype(begin(std::declval<T>()))> drop_begin(T &&t, int n) {
-  return make_range(std::next(begin(t), n), end(t));
+template <typename T>
+iterator_range<decltype(adl_begin(std::declval<T>()))> drop_begin(T &&t,
+                                                                  int n) {
+  return make_range(std::next(adl_begin(t), n), adl_end(t));
 }
 }
 
diff --git a/llvm/unittests/ADT/IteratorTest.cpp b/llvm/unittests/ADT/IteratorTest.cpp
@@ -387,4 +387,17 @@ TEST(RangeTest, Distance) {
   EXPECT_EQ(std::distance(v2.begin(), v2.end()), size(v2));
 }
 
+TEST(IteratorRangeTest, DropBegin) {
+  SmallVector<int, 5> vec{0, 1, 2, 3, 4};
+
+  for (int n = 0; n < 5; ++n) {
+    int i = n;
+    for (auto &v : drop_begin(vec, n)) {
+      EXPECT_EQ(v, i);
+      i += 1;
+    }
+    EXPECT_EQ(i, 5);
+  }
+}
+
 } // anonymous namespace

Original file line number	Diff line number	Diff line change
`@@ -59,9 +59,10 @@ template <typename T> iterator_range<T> make_range(std::pair<T, T> p) {`
`59`	`59`	`return iterator_range<T>(std::move(p.first), std::move(p.second));`
`60`	`60`	`}`
`61`	`61`
`62`		`-template<typename T>`
`63`		`-iterator_range<decltype(begin(std::declval<T>()))> drop_begin(T &&t, int n) {`
`64`		`- return make_range(std::next(begin(t), n), end(t));`
	`62`	`+template <typename T>`
	`63`	`+iterator_range<decltype(adl_begin(std::declval<T>()))> drop_begin(T &&t,`
	`64`	`+ int n) {`
	`65`	`+ return make_range(std::next(adl_begin(t), n), adl_end(t));`
`65`	`66`	`}`
`66`	`67`	`}`
`67`	`68`