Which of the below two should be preferred and why?
struct X {
Y data_;
explicit X(Y&& data): data_(std::forward<Y>(data)) {}
};
vs
struct X {
Y data_;
explicit X(Y data): data_(std::move(data)) {}
};
The two variants differ in functionality. The following statements work for the second one–but not for the first one:
Y y;
X x(y);
If you are looking for the same functionality, the two variants should look as follows:
struct X
{
Y data_;
explicit X(const Y& data) : data_(data) { }
explicit X(Y&& data) : data_(std::move(data)) { }
};
struct X
{
Y data_;
explicit X(Y data) : data_(std::move(data)) { }
};
The first variant saves one move operation, whereas the second variant is less to write. So, the answer is: Use the latter as long as you have no reason to optimize the performance.