Re: [boost] Re: container design (Was: std::complex design (Was: N-Dimensional array))

From: Howard Hinnant (hinnant_at_[hidden])
Date: 2002-03-07 19:17:12

This proposal looks good to me.

On Thursday, March 7, 2002, at 06:10  PM, rwgk wrote:

> If we suppress the construction of the elements, where
> could we get into trouble later (assuming that the user has
> explicitly requested uninitialized initialization and is
> therefore responsible for other side effects)?
> Isn't the answer: Only if T has a non-trivial destructor?
> What else could go wrong?

Just one nit:

I think this is the wrong question.  I can imagine a class with a 
non-trivial construction process but a trivial destruction process.  For 
example a class that must keep a pointer to some part of itself to 
satisfy a class invariant.  The pointer must be set in a constructor.  
But the destructor is a no-op.  Such a class should not be used with 
uninitialized_flag.  That makes 
BOOST_STATIC_ASSERT(boost::has_trivial_destructor<T>::value);
nothing but false security.

I would propose either programmer beware, and have no checks.  Or that a 
traits be developed that says:  this class has a constructor that is a 
no-op.  It is the construction we're skipping.  If the class can't be 
constructed with 0 instructions, then we shouldn't be trying to do 
that.  vector<T>(N, uninitialized_flag) still represents N /constructed/ 
T's.  It's just that their value is indeterminant.

-Howard