Add range based wrapper around std::for_each.

[kpw]

Summary

There are a few range based wrappers llvm provides already. They're handy and I
couldn't find one for std::for_each, so I'm adding it.

[kpw]

David Blakie convinced me over email that std::for_each doesn't add value over ranged based for.

include/llvm/ADT/STLExtras.h

auto find_if(R &&Range, UnaryPredicate P) -> decltype(std::begin(Range)) {
   return std::find_if(std::begin(Range), std::end(Range), P);
 }
 
 template <typename R, typename UnaryPredicate>
 auto find_if_not(R &&Range, UnaryPredicate P) -> decltype(std::begin(Range)) {
   return std::find_if_not(std::begin(Range), std::end(Range), P);
 }
 
+/// Provide wrapper to std::for_each which take ranges instead of having to
+/// pass begin/end explicitly.
+template <typename R, typename UnaryFunction>
+UnaryFunction for_each(R &&Range, UnaryFunction F) {
+  return std::for_each(std::begin(Range), std::end(Range), F);
+}
+
 /// Provide wrappers to std::remove_if which take ranges instead of having to
 /// pass begin/end explicitly.
 template <typename R, typename UnaryPredicate>
 auto remove_if(R &&Range, UnaryPredicate P) -> decltype(std::begin(Range)) {
   return std::remove_if(std::begin(Range), std::end(Range), P);
 }
 
 /// Provide wrappers to std::copy_if which take ranges instead of having to

unittests/ADT/STLExtrasTest.cpp

TEST(STLExtrasTest, EraseIf) {
   erase_if(V, [](int i) { return i % 2 == 0; });
   EXPECT_EQ(4u, V.size());
   EXPECT_EQ(1, V[0]);
   EXPECT_EQ(3, V[1]);
   EXPECT_EQ(5, V[2]);
   EXPECT_EQ(7, V[3]);
 }
 
+TEST(STLExtrasTest, ForEach) {
+  std::vector<std::pair<int, int>> V = {{1, 2}, {3, 4}, {5, 6}};
+  std::vector<int> Evens{};
+  auto BackInserter = std::back_inserter(Evens);
+  for_each(V,
+           [&](std::pair<int, int> Element) { BackInserter = Element.second; });
+  std::vector<int> ExpectedEvens = {2, 4, 6};
+  EXPECT_EQ(Evens, ExpectedEvens);
+}
+
 }