Re: [boost] auto_vector - vector with auto_ptr semantics

From: Howard Hinnant (hinnant_at_[hidden])
Date: 2002-02-05 13:53:50

On Tuesday, February 5, 2002, at 01:36  PM, Hamish Mackenzie wrote:

>> However if the vector uses 1 (move construct) to move the elements out
>> of the way, and an exception is thrown while copy assigning x into
>> place, then the vector is still in a valid state.  There are no holes 
>> of
>> uninitialized memory.  Basic exception safety has been maintained.
>
> But even 1 will leave the source damaged will it not?  So an exception
> could still lead to double destruction of the same object.

Nope.  Use of #1 to move elements from the end into the unused capacity 
leaves a vector that is longer than the original with a region of 
elements in a (for example) default state in the middle.  With #3 these 
middle elements are destructed.  This half way state must either be 
valid, or it must be clean-up-able as one starts to copy the argument x 
in.  I much prefer to keep the vector in a valid state at all times.  
This approach produces much cleaner, tighter code than doing a try/catch 
and then putting things back in order in the catch clause.

-Howard