Re: [boost] Improving the assignment operators of various Boosttypes

Subject: Re: [boost] Improving the assignment operators of various Boosttypes
From: Niels Dekker - mail address until 2008-12-31 (nd_mail_address_valid_until_2008-12-31_at_[hidden])
Date: 2008-09-11 05:07:42

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);

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...

Kind regards, Niels