How Can Move Semantics Be Enforced During Vector Growth in C ?

Enforcing Move Semantics in Vector Growth

In C , it's essential to consider object semantics when manipulating data structures like vectors. By default, vectors utilize copy constructors to fill-up with new elements. However, in certain scenarios, enforcing the use of move semantics can be advantageous.

To enforce move semantics in vector expansion, one must ensure that the class in question, in this case A, has move constructors and destructors declared as noexcept. This assures the C standard library (specifically, std::vector) that these operations do not throw exceptions.

Here's an example of a move constructor that is recognized by std::vector:

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

By declaring the move constructor noexcept, std::vector is permitted to invoke it when growing the vector, resulting in the efficient transfer of resources rather than incurring the overhead of copying.

Alternative approaches include utilizing emplace_back when feasible. This method can provide performance benefits or enhance code clarity. However, it warrants caution, particularly with non-explicit constructors.

Finally, the default behavior for vectors is to prioritize moving movable elements and copying the remainder. To explicitly enforce this, declare the move constructor as follows:

A(A&& rhs) = default;

This declaration ensures noexcept when possible, leveraging the default behavior that balances efficiency and compatibility. Note that older versions of Visual Studio 2015 and earlier may not fully support this feature despite their support for move semantics.

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