What needs to be done to invoke optimal move semantics when redistributing elements in std::vector?

To invoke optimal move semantics when reallocating elements in std::vector, the element type must support a move constructor and move assignment operator.

When adding new elements or reallocating memory, std::vector will use the move constructor instead of copying if it is available and not deleted.

To ensure moving occurs, you should:

• Define a move constructor and move assignment operator for the element type.
• Make sure they are not deleted or disabled.
• Use methods that support moving, such as emplace_back or push_back(std::move(obj)).

Example:

#include <vector>
#include <string>

struct MyType {
    std::string data;
    MyType(std::string d) : data(std::move(d)) {}
    MyType(MyType&& other) noexcept = default; // move constructor
    MyType& operator=(MyType&& other) noexcept = default; // move assignment operator
};

int main() {
    std::vector<MyType> v;
    v.emplace_back("example"); // constructs object directly in vector
    MyType obj("test");
    v.push_back(std::move(obj)); // invokes move
}

Thus, having and correctly implementing move constructors and operators allows std::vector to efficiently move elements during reallocation.