make mapped iterator smaller by using the no_unique_address optimization

commit_hash:42520e745ec2135e405740d2591c55b70b0cba43

3 files changed, 23 insertions, 4 deletions

diff --git a/library/cpp/iterator/filtering.h b/library/cpp/iterator/filtering.h
index c28e3bc6c44..23cfef6d70e 100644
--- a/library/cpp/iterator/filtering.h
+++ b/library/cpp/iterator/filtering.h
@@ -2,6 +2,7 @@
 
 #include <util/generic/iterator_range.h>
 #include <util/generic/store_policy.h>
+#include <util/system/compiler.h>
 #include <iterator>
 
 
@@ -53,7 +54,7 @@ private:
     }
     TIterator Iter;
     TIterator Last;
-    TCondition Condition;
+    Y_NO_UNIQUE_ADDRESS TCondition Condition;
 };
 
 
@@ -87,7 +88,7 @@ public:
 
 private:
     mutable TContainerStorage Container;
-    mutable TConditionStorage Condition;
+    Y_NO_UNIQUE_ADDRESS mutable TConditionStorage Condition;
 };
 
 
diff --git a/library/cpp/iterator/mapped.h b/library/cpp/iterator/mapped.h
index d78371a9e5d..348aa200bf2 100644
--- a/library/cpp/iterator/mapped.h
+++ b/library/cpp/iterator/mapped.h
@@ -2,6 +2,7 @@
 
 #include <util/generic/iterator_range.h>
 #include <util/generic/store_policy.h>
+#include <util/system/compiler.h>
 
 #include <iterator>
 
@@ -91,7 +92,7 @@ public:
 
 private:
     TIterator Iter;
-    TMapper Mapper;
+    Y_NO_UNIQUE_ADDRESS TMapper Mapper;
 };
 
 
@@ -130,7 +131,7 @@ public:
 
 protected:
     mutable TContainerStorage Container;
-    mutable TMapperStorage Mapper;
+    Y_NO_UNIQUE_ADDRESS mutable TMapperStorage Mapper;
 };
 
 
diff --git a/library/cpp/iterator/ut/mapped_ut.cpp b/library/cpp/iterator/ut/mapped_ut.cpp
index 440cd37945a..15a8196eded 100644
--- a/library/cpp/iterator/ut/mapped_ut.cpp
+++ b/library/cpp/iterator/ut/mapped_ut.cpp
@@ -7,12 +7,29 @@
 
 using namespace testing;
 
+namespace {
+    struct TSelectFirst {
+        const auto& operator()(const auto& pair) const {
+            return pair.first;
+        }
+    };
+}
+
 TEST(TIterator, TMappedIteratorTest) {
     TVector<int> x = {1, 2, 3, 4, 5};
     auto it = MakeMappedIterator(x.begin(), [](int x) { return x + 7; });
 
     EXPECT_EQ(*it, 8);
     EXPECT_EQ(it[2], 10);
+
+    TVector<std::pair<int, int>> pairs = {{1, 2}, {3, 4}, {5, 6}};
+    auto firstIt = MakeMappedIterator(pairs.begin(), TSelectFirst{});
+    EXPECT_EQ(*std::next(firstIt, 0), 1);
+    EXPECT_EQ(*std::next(firstIt, 1), 3);
+    EXPECT_EQ(*std::next(firstIt, 2), 5);
+#if defined(_compiler_clang_) && defined(_linux_)
+    static_assert(sizeof(pairs.begin()) == sizeof(firstIt), "empty mapper should not add size overhead");  // this check expected to hold, but not guaranteed to
+#endif
 }
 
 TEST(TIterator, TMappedRangeTest) {