Re: [Boost-users] (no subject)

From: John Maddock (john_at_[hidden])
Date: 2008-03-22 05:58:08

Richard Webb wrote:
> Kevin Scarr <kscarr <at> iinet.net.au> writes:
>
>>
>> My code compiles, and appears to work fine, however, I am always
>> nervous about these kinds of warnings because I suspect there is
>> something waiting to bite me. I guess I am concerned as to what in
>> my code is causing the compiler to want to generate assignment
>> operators.
>>
>> Are these warnings symptomatic of a basic mistake I am making? I know
>> that you can't see the code, so this is only a general question. If
>> people think this might be a real problem, I am happy to try to make
>> a small code snippet to illustrate the problem.
>>
>
> The ASIO warning you're seeing is because the struct in question
> (auto_work) has a reference as a member.
> VC8/9 produce loads of similar warnings on Boost code. They cause a
> lot of noise, but don't seem to cause any real problems.

Actually I'm pretty annoyed that these warnings are generated by the 
compiler at all: as far as I can see they can never represent a true 
programming error - though I stand to be corrected on that one!

The warnings are raised when a class or structure does *not* have an 
explicit copy-constructor or assignment operator declared, *and* one could 
not be generated automatically by the compiler.  However, the warnings are 
issued even though neither the copy-constructor nor the assignment operator 
are ever used - if they were used then you would get a compiler error.

One possible fix is to declare but not define a private copy constructor and 
assignment operator (rather like boost::noncopyable), but given that those 
definitions are never used, this is just syntactic sugar to shut the 
compiler up.  BTW if I remember correctly you get the same warnings if you 
declare a class that inherits from noncopyable which rather destroys the 
whole point of that one :-(

Tellingly, as far as I know VC++ is the only compiler to issue this warning.

HTH, John.