allow lambdas in mapped_iterator

[aizatsky]

Summary

::result_type is undefined for lambdas, but we now have decltype!

[sanjoy]

This looks okay to me, but I don't know enough C++ to have an idea of the corner cases here.

[dblaikie]

Got a test/usage example?

[aizatsky]

added unittest.

[aizatsky]

I have added the unittest for map_iterator. My final goal is to move map_range somewhere, but I was planning to do it in next CL.

[dblaikie]

Looks good to me - thanks!

(I'd probably just include one of those two tests - not like the test new/unique/separate codepaths really, but I'm not too fussed)

[aizatsky]

I had to roll it back because of MSVC:

C:\Buildbot\Slave\llvm-clang-lld-x86_64-scei-ps4-windows10pro-fast\llvm.src\include\llvm/ADT/STLExtras.h(120): error C2100: illegal indirection
C:\Buildbot\Slave\llvm-clang-lld-x86_64-scei-ps4-windows10pro-fast\llvm.src\include\llvm/IR/Instructions.h(3966): note: see reference to class template instantiation 'llvm::mapped_iterator<llvm::User::op_iterator,llvm::CatchSwitchInst::DerefFnTy>' being compiled

include/llvm/ADT/STLExtras.h

 class mapped_iterator {
   RootIt current;
   UnaryFunc Fn;
 public:
   typedef typename std::iterator_traits<RootIt>::iterator_category
           iterator_category;
   typedef typename std::iterator_traits<RootIt>::difference_type
           difference_type;
-  typedef typename UnaryFunc::result_type value_type;
+  typedef decltype(Fn(*current)) value_type;
 
   typedef void pointer;
   //typedef typename UnaryFunc::result_type *pointer;
   typedef void reference;        // Can't modify value returned by fn
 
   typedef RootIt iterator_type;
 
   inline const RootIt &getCurrent() const { return current; }

unittests/ADT/CMakeLists.txt

set(ADTSources
   HashingTest.cpp
   ilistTest.cpp
   ImmutableMapTest.cpp
   ImmutableSetTest.cpp
   IntEqClassesTest.cpp
   IntervalMapTest.cpp
   IntrusiveRefCntPtrTest.cpp
   MakeUniqueTest.cpp
+  MappedIteratorTest.cpp
   MapVectorTest.cpp
   OptionalTest.cpp
   PackedVectorTest.cpp
   PointerEmbeddedIntTest.cpp
   PointerIntPairTest.cpp
   PointerSumTypeTest.cpp
   PointerUnionTest.cpp
   PostOrderIteratorTest.cpp

unittests/ADT/MappedIteratorTest.cpp

+//===- llvm/unittest/ADT/APInt.cpp - APInt unit tests ---------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include <vector>
+
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/iterator_range.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace {
+
+template <class T, class Fn>
+auto map_range(const T &range, Fn fn)
+    -> decltype(make_range(map_iterator(range.begin(), fn),
+                           map_iterator(range.end(), fn))) {
+  return make_range(map_iterator(range.begin(), fn),
+                    map_iterator(range.end(), fn));
+}
+
+static char add1(char C) { return C + 1; }
+
+TEST(MappedIterator, FnTest) {
+  std::string S("abc");
+  std::string T;
+
+  for (char C : map_range(S, add1)) {
+    T.push_back(C);
+  }
+
+  EXPECT_STREQ("bcd", T.c_str());
+}
+
+TEST(MappedIterator, LambdaTest) {
+  std::string S("abc");
+  std::string T;
+
+  for (char C : map_range(S, [](char C) { return C + 1; })) {
+    T.push_back(C);
+  }
+
+  EXPECT_STREQ("bcd", T.c_str());
+}
+}