How were move semantics addressed before C++11?

Question

I\'ve been reading up on move semantics lately and how it was introduced into C++11. The main gist is that programs could become more efficient by creating objects by \'stealing

Answer 1

The main way this was done was via std::swap. std::swap could be overloaded/specialized for types where it could be executed more efficiently than the default "swap via a temporary variable" to instead perform a shallow swap.

Often data types would provide a swap() member function that could be used by this overload to access the private internals of the data type. (For example; see std::vector::swap)

For example; to "move" an element into a vector, the following code could be used:

class MyListOfVectors {
    private:
    //using `std::vector<int>` as an example of a "movable" type.
    std::vector<std::vector<int>> list;
    public:
    void emplace_back(std::vector<int> &n) {
        using std::swap;
        list.push_back(std::vector<int>());
        swap(list.back(), n);
        //(possibly add something to rollback the `push`
        // in case swap fails; to provide the strong
        // exception guarantee)
    }
};

To return an element via "move", the following code could be used:

std::vector<int> MyListOfVectors::pop_back() {
    using std::swap;
    std::vector<int> r;
    swap(list.back(), r);
    list.pop_back();
    return r; //Trust in copy elision to avoid any actual copies.
}

I don't have a reference for this, but I believe standard algorithms were allowed/encouraged to use std::swap for this purpose.

Also, if you were feeling like you wanted to do things the C++11 way, you could also use boost::move, which provides an emulation of the C++11 move semantics in C++03 (though it technically violates strict aliasing and so has undefined behavior).