Re: [boost] several messages

Subject: Re: [boost] several messages
From: Marc Glisse (marc.glisse_at_[hidden])
Date: 2012-08-05 07:39:35

On Sun, 5 Aug 2012, John Maddock wrote:

>> Uh?
>> This is indeed what happens, but for GMP types, unless you added in your 
>> wrapper a special 0 state (which you then have to test in every operation), 
>> every constructor has to allocate, including the move constructor, since a 
>> moved-from object must still be in a valid state.
>> 
>> Did you add an empty state then?
>
> The move constructor doesn't allocate - it takes ownership of the GMP 
> variable, and sets the variable in the moved-from object to a null state. The 
> *destructor* then has an added check to ensure it doesn't try and clear null 
> GMP objects: that's basically the only change.  IMO the cost of the extra if 
> statement in the destructor is worth it - and should be trivial compared to 
> calling the external library routine to clear the GMP variable.

Well, what happens then if you do something to a moved-from object other 
than destructing it?

number a=2;
number b=move(a);
a=2; // or a=b; or a=b+1; or ...

-- 
Marc Glisse