[PATCH] D138858: [ADT] Clarify `zip` behavior with iteratees of different lengths. NFC.

[Jakub Kuderski via Phabricator via llvm-commits]

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Update the documention comment and add a new test case.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D138858

Files:
  llvm/include/llvm/ADT/STLExtras.h
  llvm/unittests/ADT/IteratorTest.cpp


Index: llvm/unittests/ADT/IteratorTest.cpp
===================================================================
--- llvm/unittests/ADT/IteratorTest.cpp
+++ llvm/unittests/ADT/IteratorTest.cpp
@@ -395,16 +395,25 @@
   const SmallVector<unsigned, 6> pi{3, 1, 4, 1, 5, 9};
   SmallVector<bool, 6> odd{1, 1, 0, 1, 1, 1};
   const char message[] = "yynyyy\0";
+  std::array<int, 2> shortArr = {42, 43};
 
   for (auto tup : zip(pi, odd, message)) {
     EXPECT_EQ(get<0>(tup) & 0x01, get<1>(tup));
     EXPECT_EQ(get<0>(tup) & 0x01 ? 'y' : 'n', get<2>(tup));
   }
 
-  // note the rvalue
+  // Note the rvalue.
   for (auto tup : zip(pi, SmallVector<bool, 0>{1, 1, 0, 1, 1})) {
     EXPECT_EQ(get<0>(tup) & 0x01, get<1>(tup));
   }
+
+  // Iterate until we run out elements in the *shortest* range.
+  for (auto [idx, elem] : enumerate(zip(odd, shortArr))) {
+    EXPECT_LT(idx, static_cast<size_t>(2));
+  }
+  for (auto [idx, elem] : enumerate(zip(shortArr, odd))) {
+    EXPECT_LT(idx, static_cast<size_t>(2));
+  }
 }
 
 TEST(ZipIteratorTest, ZipFirstBasic) {
Index: llvm/include/llvm/ADT/STLExtras.h
===================================================================
--- llvm/include/llvm/ADT/STLExtras.h
+++ llvm/include/llvm/ADT/STLExtras.h
@@ -870,19 +870,21 @@
 
 } // end namespace detail
 
-/// zip iterator for two or more iteratable types.
+/// zip iterator for two or more iteratable types. Iteration continues until the
+/// end of the *shortest* iteratee is reached.
 template <typename T, typename U, typename... Args>
 detail::zippy<detail::zip_shortest, T, U, Args...> zip(T &&t, U &&u,
-                                                       Args &&... args) {
+                                                       Args &&...args) {
   return detail::zippy<detail::zip_shortest, T, U, Args...>(
       std::forward<T>(t), std::forward<U>(u), std::forward<Args>(args)...);
 }
 
 /// zip iterator that, for the sake of efficiency, assumes the first iteratee to
-/// be the shortest.
+/// be the shortest. Iteration continues until the end of the first iteratee is
+/// reached.
 template <typename T, typename U, typename... Args>
 detail::zippy<detail::zip_first, T, U, Args...> zip_first(T &&t, U &&u,
-                                                          Args &&... args) {
+                                                          Args &&...args) {
   return detail::zippy<detail::zip_first, T, U, Args...>(
       std::forward<T>(t), std::forward<U>(u), std::forward<Args>(args)...);
 }


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