The efficient way to write move copy and move assignment constructors

Question

Are the following assignment and copy move constructors the most efficient? if anybody have other way please tell me? I mean what bout std::swap? and calling assignment th

Answer 1

You don't need so many swaps and assignments in your move constructor. This:

Widget(Widget&& other) :
    length( other.length_ ), data( other.data_ )
{
    other.length_ = 0;
    other.data_ = nullptr;
}

does the minimum work for the move constructor: 4 assignments in total. Your version had 8, counting the ones in the calls to swap().

Your move assignment is OK, but you might want to consider just writing one operator=() to cover both cases:

Widget &operator=( Widget other ) {
    delete data_;
    data_ = other.data_;
    other.data_ = nullptr;
    length_ = other.length_;
    other.length_ = 0;
    return *this;
}

This is slightly less efficient than your version, in that it can move twice.