On Thu, Sep 11, 2008 at 11:07 AM, Niels Dekker - mail address until 2008-12-31 <nd_mail_address_valid_until_2008-12-31@xs4all.nl> wrote:
David Abrahams wrote:
In generic code I strongly prefer
T& operator=(T arg) { swap(*this, arg); return *this; }
I'm just saying, I guess, that the form using the member forces me to define a swap member even though it's not really needed by generic code.
I think we should stick to the guideline to always have a swap member function for a class, whenever the class has a custom free swap function. Don't you agree?
BTW the swap member function offers a C++03 way to "move assign" an rvalue:
std::vector<int> generate_some_data(void); std::vector<int> my_data; // Move the result into my_data: generate_some_data().swap(my_data);
I guess this is a common idiom, I use it a lot. OTOH if my_data::operator=() used pass by value (which in the case of standard containers is, unfortunately, not true), the member swap wouldn't be necessary. In practice this means that, for your own classes, or you implement the 'smart' operator= or you need the member swap (to swap out of temporaries). You do not need both. -- gpd