on Thu Sep 11 2008, "Niels Dekker - mail address until 2008-12-31" <nd_mail_address_valid_until_2008-12-31-AT-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?
Sorry, but no, I just don't see the point. It feels like needless clutter. Generic code needs a free function that can be found via ADL, so I would normally make it a friend declared inside the class body. There's nothing wrong with adding a swap member, but I'd be loathe to make it a guideline.
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);
Well, that's true, but I much prefer: assign(my_data) = generate_some_data(); because it better reflects the logical operation.
Peter Dimov wrote:
Incidentally: http://aspn.activestate.com/ASPN/Mail/Message/boost/1140338> "It doesn't compile with Borland C++Builder 4 or BCC 5.5.
The next problem was associative_vector's assignment operator. Borland didn't recognise it as one and generated a default. Then it couldn't disambiguate the generated assignment operator and the one supplied. [...]
My memory is correct on this one, too. I'm not sure why BCC 5.5.1 didn't exhibit the problem in my tests.
Thanks Peter. Maybe it's a C++Builder 4/BCC 5.5 bug that was fixed by BCC 5.5.1. :-) Anyway, neither of them are still at the regression pages. Siliconman runs the tests on BCC 5.6.4, 5.8.2, and 5.9.3, while JustSoftwareSolutions does BCC 5.8.2.
Thanks Joaquín, for already applying the patch from ticket #2313 to multi_index_container::operator= Things still look fine at the regression page <www.boost.org/development/tests/trunk/developer/multi_index.html> but I guess we have to wait a few days longer...
Niels: are you planning to pursue tickets for the classes with implicit assignment operators and the others I mentioned in response to your original post? -- Dave Abrahams BoostPro Computing http://www.boostpro.com