Why Does `std::move` Work on Constant Objects in C ?

Why Can We Call std::move on a const Object?

C 11 introduced the std::move function to support moving semantics. This raised a question: why can std::move be used on constant objects?

If we attempt to move a constant object, it seems like we are trying to alter it, which wouldn't make sense. However, std::move cleverly does not actually move anything. Instead, it instructs the compiler to attempt to move the object.

If the class of the object has a move constructor, the move will occur as expected. But if the class doesn't, the compiler will instead use the copy constructor, ensuring that the constant object is safely copied.

For example:

struct Cat {
  Cat() {}
};

const Cat cat;
Cat cat2 = std::move(cat);

In this case, the std::move will fall back to the copy constructor, printing "COPY" instead of "MOVE" if a std::cout is added to the constructors.

std::move's behavior on constant objects is not a trap, but a feature. It allows for efficient move attempts without risking the stability of the program. Additionally, not all code relies on move semantics, so allowing std::move to operate on constant objects provides flexibility.

The above is the detailed content of Why Does `std::move` Work on Constant Objects in C ?. For more information, please follow other related articles on the PHP Chinese website!