Re: [boost] Re: Re: Re: Re: Boost Array Initialization Technique

From: christopher diggins (cdiggins_at_[hidden])
Date: 2005-05-31 23:46:20

"Jonathan Turkanis" <technews_at_[hidden]> wrote in message 
news:d7j8it$1pt$1_at_sea.gmane.org...
> christopher diggins wrote:
>
>> violates the container postconditions. Just for example consider the
>> following common idiom:
>>
>> template<class Container_T>
>> void some_very_dangerous_code(Container_T& x) {
>>   x = Container_T();
>>   if (x.empty()} {
>>     SayHelloToAlphaCentauri();
>>   }
>>   else {
>>     SendNukesToAlphaCentauri();
>>   }
>> }
>>
>> Obviously this will not work as expected.
>
> What's expected here?

What was expected was that the SendNukesToAlphaCentauri() control path 
should never be executed BUT I made a big mistake (and a common one at 
that). I assumed x == y implied x.size() == y.size() for standard 
containers. That is not in fact an explicit postcondition of containers as 
far as I know. Since the example is unsatisfactory here is another:

template<class Container_T>
void some_very_dangerous_code() {
  Container_T x();
  if (x.empty()} {
   SayHelloToAlphaCentauri();
  }
  else {
   SendNukesToAlphaCentauri();
  }
}

The point is not whether or not this is a good example but rather that 
incorrect and unexpected (possibly disastrous) behaviour will be exhibited 
in existing code by using a non-conformant container in a context where a 
conformant container is expected.

-- 
Christopher Diggins
http://www.cdiggins.com