Re: [boost] Review of a safer memory management approach for C++?

Subject: Re: [boost] Review of a safer memory management approach for C++?
From: David Abrahams (dave_at_[hidden])
Date: 2010-06-05 09:56:38

on Fri Jun 04 2010, "Bartlett, Roscoe A" <rabartl-AT-sandia.gov> wrote:

> David,
>
> From: David Abrahams [mailto:dave_at_[hidden]]
>> The whole notion of deep-vs-shallow copy is a fallacy.  If you nail
>> down what it means to make a “copy”---which will force you to nail
>> down what constitutes an object's value---you'll see that.
>
> [Bartlett, Roscoe A] 
>
> It is not a fallacy.  The only obvious behavior for value semantics is deep copy such
> that if you do:
>
>    A a(...);
>    B b = a;
>
> then any change to 'b' will have *no* impact on the behavior of 'a' at
> all, period.

And that, right there, is the definition of “copy” (assuming A and B are
the same type).  There's no such thing as a “shallow copy” of a that's
different from what you just described.

> Anything else is not value semantics and will confuse people.  Make it simple; most
> types should have either value semantics or reference semantics as described in
> Section 4.1 in the Teuchos MM report.  Anything in between is just confusing and
> counter-intuitive.

Your “reference types” as defined there are not copyable, so there's no
“shallow copy” going on.  Period.  Viewing it that way makes it *really*
simple. :-)

Cheers,

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