Re: [boost] [proposal] raw move

Subject: Re: [boost] [proposal] raw move
From: Dave Abrahams (dave_at_[hidden])
Date: 2011-08-24 00:53:14

on Tue Aug 23 2011, Ion Gaztañaga <igaztanaga-AT-gmail.com> wrote:

> El 23/08/2011 17:17, Christopher Jefferson escribió:
>
>> When moving was originally discussed, things like 'destructive' and
>> 'raw' moves were discussed, but it was decided in the end they were
>> too dangerous, without proving substantial benefits. For example, you
>> can rearrange a list of std::vectors with memcpy, but if you get half
>> way through and an exception is thrown and you end up with the same
>> vector left in two places in memory, horrible things will happen as
>> they will refer to the same memory block.
>
> IMHO, destructive move should be required always to be no-throw.

Destructive move is practically impossible to manage regardless of
exceptions:

        void f()
        {
            SomeType x;

            if (some_condition)
            {
                something_that_moves(x)
            }
            else
            {
                x.foo()
            }
            // Do we call x's destructor?
        }

Even if you say the compiler can solve the problem in that trivial case
I can easily come up with slightly-less-trivial cases where the problem
arises and is absolutely intractable.

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com