Add emplace_back, move_assignment to BoundedVector (#385)

* Add emplace_back, move_assignment to BoundedVector

Signed-off-by: Christopher Ho <christopherj.ho@gmail.com>

* Address reviewer comments:

- Use `auto` for portability
- Add unit tests
- Add documentation

Signed-off-by: Christopher Ho <christopher.ho@apex.ai>

rosidl_generator_cpp/include/rosidl_generator_cpp/bounded_vector.hpp

@@ -207,8 +207,18 @@ class BoundedVector
   BoundedVector &
   operator=(const BoundedVector & __x)
   {
-    reinterpret_cast<std::vector<_Tp, _Alloc> *>(this)->operator=(
-      *reinterpret_cast<const std::vector<_Tp, _Alloc> *>(&__x));
+    (void)_Base::operator=(__x);
+    return *this;
+  }
+
+  /// %BoundedVector move assignment operator
+  /**
+   * \param __x A %BoundedVector of identical element and allocator types.
+   */
+  BoundedVector &
+  operator=(BoundedVector && __x)
+  {
+    (void)_Base::operator=(std::forward<_Base &&>(__x));
     return *this;
   }
 
@@ -454,6 +464,27 @@ class BoundedVector
     _Base::push_back(__x);
   }
 
+  /// Add data to the end of the %BoundedVector.
+  /**
+   * This is a typical stack operation.
+   * The function creates an element at the end of the %BoundedVector
+   * and assigns the given data to it.
+   * Due to the nature of a %BoundedVector this operation can be done in
+   * constant time if the %BoundedVector has preallocated space
+   * available.
+   *
+   * \param args Arguments to be forwarded to the constructor of _Tp
+   */
+  template<typename ... Args>
+  auto
+  emplace_back(Args && ... args)
+  {
+    if (size() >= _UpperBound) {
+      throw std::length_error("Exceeded upper bound");
+    }
+    return _Base::emplace_back(std::forward<Args>(args)...);
+  }
+
   /// Insert an object in %BoundedVector before specified iterator.
   /**
    * This function will insert an object of type T constructed with
@@ -607,6 +638,13 @@ class BoundedVector
   using _Base::erase;
   using _Base::pop_back;
   using _Base::clear;
+
+private:
+  /// Cast to base type, to make it easier to dispatch to base implementations
+  operator _Base &()
+  {
+    return *this;
+  }
 };
 
 /// Vector equality comparison.

rosidl_generator_cpp/test/test_bounded_vector.cpp

@@ -13,6 +13,7 @@
 // limitations under the License.
 
 #include <gtest/gtest.h>
+#include <utility>
 
 #include "rosidl_generator_cpp/bounded_vector.hpp"
 
@@ -32,3 +33,20 @@ TEST(rosidl_generator_cpp, bounded_vector) {
   auto l = {1, 2, 3};
   ASSERT_THROW(v = l, std::length_error);
 }
+
+TEST(rosidl_generator_cpp, bounded_vector_rvalue) {
+  rosidl_generator_cpp::BoundedVector<int, 2> v;
+  // emplace back
+  ASSERT_EQ(v.size(), 0u);
+  ASSERT_EQ(v.max_size(), 2u);
+  v.emplace_back(1);
+  v.emplace_back(2);
+  ASSERT_THROW(v.emplace_back(3), std::length_error);
+  ASSERT_EQ(v.size(), 2u);
+  // move assignment
+  decltype(v) vv;
+  vv = std::move(v);
+  ASSERT_EQ(vv.size(), 2u);
+  ASSERT_EQ(vv[0], 1);
+  ASSERT_EQ(vv[1], 2);
+}