added pop_back function to SmallVector

follow std::vector by making it undefined for empty vectors

2 files changed, 27 insertions, 0 deletions

diff --git a/vespalib/src/tests/small_vector/small_vector_test.cpp b/vespalib/src/tests/small_vector/small_vector_test.cpp
index 2118a3c492f..4b432799672 100644
--- a/vespalib/src/tests/small_vector/small_vector_test.cpp
+++ b/vespalib/src/tests/small_vector/small_vector_test.cpp
@@ -7,6 +7,14 @@
 
 using namespace vespalib;
 
+struct Alive {
+    uint32_t &cnt;
+    uint32_t id;
+    Alive(uint32_t &cnt_in, uint32_t id_in) noexcept
+      : cnt(cnt_in), id(id_in) { ++cnt; }
+    ~Alive() { --cnt; }
+};
+
 template <typename T, size_t N>
 void verify(const SmallVector<T,N> &vec, std::vector<uint32_t> expect, size_t expect_capacity = 0) {
     if (expect_capacity == 0) {
@@ -263,4 +271,22 @@ TEST(SmallVectorTest, check_back_method) {
     EXPECT_EQ(&vec.back(), vec.end() - 1);
 }
 
+TEST(SmallVectorTest, pop_back) {
+    uint32_t my_cnt = 0;
+    {
+        SmallVector<Alive> vec;
+        vec.emplace_back(my_cnt, 1);
+        vec.emplace_back(my_cnt, 2);
+        vec.emplace_back(my_cnt, 3);
+        EXPECT_EQ(vec.size(), 3);
+        EXPECT_EQ(my_cnt, 3);
+        vec.pop_back();
+        EXPECT_EQ(my_cnt, 2);
+        ASSERT_EQ(vec.size(), 2);
+        EXPECT_EQ(vec[0].id, 1);
+        EXPECT_EQ(vec[1].id, 2);
+    }
+    EXPECT_EQ(my_cnt, 0);
+}
+
 GTEST_MAIN_RUN_ALL_TESTS()
diff --git a/vespalib/src/vespa/vespalib/util/small_vector.h b/vespalib/src/vespa/vespalib/util/small_vector.h
index ba166362d33..0d204897328 100644
--- a/vespalib/src/vespa/vespalib/util/small_vector.h
+++ b/vespalib/src/vespa/vespalib/util/small_vector.h
@@ -212,6 +212,7 @@ public:
     }
     void push_back(const T &obj) { emplace_back(obj); }
     void push_back(T &&obj) { emplace_back(std::move(obj)); }
+    void pop_back() { small_vector::destroy_objects(_data + --_size, 1); }
 };
 
 template <typename T, size_t N, size_t M>