Re: [boost] Re: Standard C Library and C++ / BOOST

From: Rene Rivera (grafik.list_at_[hidden])
Date: 2004-03-30 12:05:34

Rob Stewart wrote:
> From: Rene Rivera <grafik.list_at_[hidden]>
> 
>>Gennaro Prota wrote:
>>
>>>On Sat, 27 Mar 2004 19:23:50 -0500, David Abrahams
>>><dave_at_[hidden]> wrote:
>>>
>>>>"Klaus Nowikow" <nowikow_at_[hidden]> writes:
>>>>
>>>>>Reece Dunn wrote:
>>>>>[snip]
>>>>>
>>>>>
>>>>>>  class errorcheck
>>>>>>  {
>>>>>
>>>>>[snip]
>>>>>
>>>>>>     public:
>>>>>>        inline errorcheck( int ec ): error( ec )
>>>>>>        {
>>>>>>           if( ec < 0 ) throw( *this );
>>>>>>        }
>>>>>
>>>>>Careful. Throwing an exception from a constructor
>>>>>means that the object won't be constructed (i. e., does not exist).
>>>>>So you are throwing a non-existing object here.
>>>>>
>>>>>Or am I wrong?
>>>>
>>>>You're wrong.  *this is copied before it is thrown.  Still, the idiom
>>>>above seems a bit suspicious, unless you somehow prevent derivation
>>>
>>>>from errorcheck.
>>>
>>>I can't believe you are justifying the above. You copy an object that
>>>doesn't exist yet! (The class is not a POD and has a non trivial
>>>constructor - and even if this wasn't the case...)
>>
>>I don't see how the object is not fully initialized inside its constructor?? 
>>Could you explain your objection?
> 
> 
> Until the ctor finishes -- after the closing } -- there is no
> object (see 3.8/1).

Yes the object lifetime hasn't started... but the object is initialized. Which 
according to 12.7 allows for referring to members of the object directly or 
indirectly, in this case by a copy ctor function.

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