Intermediate C++ Game Programming Tutorial 20
In this video we learn about r-value reference and move semantics, which is perhaps the most important feature that was added in the C++11 update. This is going to allow us to manage and transfer our resources in a precise and efficient manner. It is sexy as fuck and I love it.
Topics Covered
- r-values and l-values
- r-value reference function overloading
- Move constructor and move assigment
- Rule of 5
-
std::move -
std::make_move_iterator
Video Timestamp Index
- Why are move semantics relevant and important? 0:30
- Example use case: adding objects to a container using
emplace_back - Instead of deep copying every element of the container when expanding the container capacity, move semantics allow you to direct pointers in the new container to existing blocks of memory
- Example use case: adding objects to a container using
- What is an rvalue (simple definition) 2:48?
- rvalues are values that can only appear on the right hand side of an assignment operation (=), such as:
- - literals; can't appear on the left hand side:
69 = 420;doesn't make sense - - temporary return values of functions; you can't assign to it:
f() = 420;, where the signature offisint f();doesn't make sense
- lvalues are values that can appear on the left hand side of assignments; they can be assigned to, for example:
- -
int x;x=10; - -
obj.Get() = 69;<code> if the member function <code>Get()returns a reference to an integer member variable
- ..
- WORK-IN-PROGRESS
Note
If you are using Visual Studio 2017, you might notice that our move members are not being used during std::vector growth even after we have 'properly' implemented them. This is expected, so don't pay it much mind at the moment.
The reason for this is that std::vector will only use the move members if they are guaranteed not to throw any exceptions (as per the standard). This issue will be dealt with in Intermediate 22 (tutorial on exceptions). For your interest, you can enable the move optimization by declaring your move ctor as Surface( Surface&& ) noexcept. The same should be done for the move assignment and the destructor.
You might wonder why Chili had no problems in the video. In the video, Chili was using Visual Studio 2015, which does not conform to the standard in this point, so it uses the move members regardless of whether or not they are marked noexcept.
