From 6a2af3eb1dea251bd98d4d995153021a74c9cecc Mon Sep 17 00:00:00 2001
From: Michael Gottesman <mgottesman@apple.com>
Date: Sun, 4 Dec 2016 10:26:53 +0000
Subject: [PATCH] [stl-extras] Provide an adaptor of std::count for ranges.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@288619 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/ADT/STLExtras.h    |  8 ++++++++
 unittests/ADT/STLExtrasTest.cpp | 17 +++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/include/llvm/ADT/STLExtras.h b/include/llvm/ADT/STLExtras.h
index 28e1553606c..4435b46f462 100644
--- a/include/llvm/ADT/STLExtras.h
+++ b/include/llvm/ADT/STLExtras.h
@@ -639,6 +639,14 @@ bool is_contained(R &&Range, const E &Element) {
          std::end(Range);
 }
 
+/// Wrapper function around std::count to count the number of times an element
+/// \p Element occurs in the given range \p Range.
+template <typename R, typename E>
+auto count(R &&Range, const E &Element) -> typename std::iterator_traits<
+    decltype(std::begin(Range))>::difference_type {
+  return std::count(std::begin(Range), std::end(Range), Element);
+}
+
 /// Wrapper function around std::count_if to count the number of times an
 /// element satisfying a given predicate occurs in a range.
 template <typename R, typename UnaryPredicate>
diff --git a/unittests/ADT/STLExtrasTest.cpp b/unittests/ADT/STLExtrasTest.cpp
index 44c0044c25d..76881296db6 100644
--- a/unittests/ADT/STLExtrasTest.cpp
+++ b/unittests/ADT/STLExtrasTest.cpp
@@ -236,4 +236,21 @@ TEST(STLExtrasTest, ApplyTupleVariadic) {
   EXPECT_EQ("Tes", std::get<1>(Values));
   EXPECT_EQ('Y', std::get<2>(Values));
 }
+
+TEST(STLExtrasTest, CountAdaptor) {
+  std::vector<int> v;
+
+  v.push_back(1);
+  v.push_back(2);
+  v.push_back(1);
+  v.push_back(4);
+  v.push_back(3);
+  v.push_back(2);
+  v.push_back(1);
+
+  EXPECT_EQ(3, count(v, 1));
+  EXPECT_EQ(2, count(v, 2));
+  EXPECT_EQ(1, count(v, 3));
+  EXPECT_EQ(1, count(v, 4));
+}
 }