Difference between revisions of "Intermediate C++ Game Programming Tutorial 20"

Revision as of 04:57, 19 October 2019

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

Tutorial 20

• 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
• What is an rvalue (simple definition) 2:48?
  • rvalues are values that can only appear on the right hand side of an assignment operation (=)
  • For instance, literals are rvalues, they can't appear on the left hand side: 69 = 420 doesn't make sense
• 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.

Source Code

• Sprite Github Repository (for Surface code)
  

See also

• Next in series (Tutorial 21)
• Intermediate C++ Game Programming Series