How Can I Force std::vector to Use Move Semantics During Growth?

Enforcing Move Semantics During Vector Growth

When an std::vector with non-trivial elements having defined copy and move constructors grows, the default behavior is to use the copy constructor to create new element copies. To enforce the use of the move constructor instead, C must be informed that this constructor does not throw exceptions.

Implementation

To indicate that the move constructor can be called safely, declare it with the noexcept specifier:

A(A &&rhs) noexcept { 
  std::cout << "i am the move constr" << std::endl;
  ... move-assignment code ... 
}

With this modification, std::vector will prioritize using the move constructor for growth, ensuring the resources of existing elements are moved instead of copied.

Additional Information

• For more in-depth understanding, refer to the article "C Move semantics and Exceptions."
• Consider using emplace_back instead of push_back when possible, as it can offer improved performance and clarity.
• Explicitly requesting move semantics using A(A &&rhs) = default; can ensure the move constructor is marked as noexcept when possible. Some earlier versions of Visual Studio may not fully support this feature.

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